Japanese Word Formation — Prefixes, Suffixes & Compounds [JLPT N3]

Content by NTJ Kuma · Nihongo to Japan editorial team · Updated July 27, 2026

“Dissatisfaction,” “beauty,” “reading and writing” — how Japanese builds words, so you can break down long ones.

「国際化」「可能性」「話し合う」 — breaking long Japanese words apart

Do long words like 「国際化 (こくさいか)」「可能性 (かのうせい)」「話し合う (はなしあう)」 daunt you? They're all assembled from small parts: 「国際＋化」「可能＋性」「話し＋合う」. Grasp Japanese word formation — prefixes (added at the front), suffixes (added at the end), compounds (two words merged) — and you can decompose and guess the meanings of countless long words you've never studied. This guide teaches the three word-formation methods and their common parts.

Core: break a long word into ‘prefix ＋ stem ＋ suffix' or ‘word ＋ word'

Most long Japanese words break into a few meaningful parts:

• prefix ＋ stem: added at the front to change the meaning (不便 = inconvenient; お茶 = tea [beautified]).
• stem ＋ suffix: added at the end to change part of speech or meaning (高さ = height; 国際化 = internationalization; 科学的 = scientific).
• compound = word ＋ word: two words merged into one (話し＋合う = discuss; 春＋風 = spring breeze).

Method: meet a long word, first find the common part at the front/end (お・不・化・性・的…) and split it off; what's left is the stem. Know the parts' meanings and you can infer the whole word. This greatly helps reading and vocabulary growth.

Common prefixes (added at the front)

Common suffixes (added at the end)

Compounds: two words merged

A compound merges two words into one, in several common combinations:

• verb continuative ＋ verb: 話し＋合う→話し合う (discuss); 飛び＋込む→飛び込む (jump in); 取り＋消す→取り消す (cancel).
• verb continuative ＋ noun: 乗り＋場→乗り場 (boarding area); 食べ＋物→食べ物 (food); 読み＋方→読み方 (reading/way to read).
• noun ＋ noun: 本＋棚→本棚 (bookshelf); 花＋見→花見 (flower viewing).
• adjective stem ＋ noun: 若＋者→若者 (young person); 長＋話→長話 (a long talk).

Note ‘rendaku' (sequential voicing): when two words join, the first kana of the second word often becomes voiced — 手 (て) ＋ 紙 (かみ) → 手紙 (てがみ); 花 (はな) ＋ 火 (ひ) → 花火 (はなび); 時 (とき) ＋ 々 → 時々 (ときどき). A compound whose reading turns voiced is usually rendaku.

⚠️ Common mistakes to avoid

① 「〜さ」 (objective degree) vs 「〜み」 (subjective feel). Both turn an adjective into a noun, with different feel. 〜さ = an objective, measurable ‘degree' (高さ = height [measurable]; 大きさ = size; 重さ = weight); 〜み = a subjective ‘sense/flavor,' with feeling or state (深み = depth/richness; 甘み = sweetness [as a flavor]; 温かみ = warmth [of feeling]; 痛み = pain). For an objective measurement use さ, for a subjective feel/nuance use み. Note: not every adjective takes み (only certain ones), while さ is nearly universal.

② Don't confuse 「〜的」 (→ na-adjective) with 「〜性」 (→ noun). 〜的 = turns a noun into a na-adjective, ‘…-like, having the nature of …' (科学的な考え = scientific thinking; 積極的 = positive/active); 〜性 = turns a word into a noun, ‘the quality of …, possibility' (安全性が高い = high safety; 可能性 = possibility). 「的」 is often followed by a noun or だ (科学的だ); 「性」 is itself a noun (可能性がある). To modify use 「的」, to state a “…-ness” noun use 「性」.

③ Mind reading changes when compounding/adding parts (rendaku・sound shifts). Readings often shift in word formation — rendaku (the second word voices: 手紙てがみ), gemination (真＋赤→真っ赤まっか), vowel-length shifts, etc. So the same kanji may read differently in different words (花: はな／花火はなび). When learning words, memorize the reading along with them; don't assume a part's reading never changes.

💡 The key point in use

You needn't brute-force long Japanese words — learning to decompose does the heavy lifting: ① prefixes (front: お・ご beautifying; 不・無・非・未 negating; 真・大・小 degree); ② suffixes (end, changing part of speech: 〜的→na-adjective, 〜性/さ/み→noun, 〜化→change, 〜家/屋→person, 〜中→in/all over); ③ compounds (two words merged: 話し合う, 食べ物, 若者). Three practical points: ① 「さ」 is objective degree, 「み」 subjective feel (高さ vs 深み); ② 「的」 makes a na-adjective, 「性」 a noun (科学的 vs 可能性); ③ mind rendaku when compounding (手紙てがみ, 花火はなび). Meet an unfamiliar long word, split off the front/end parts first — knowing the parts lets you guess the gist. This is a key skill for rapid vocabulary growth.

❓ Quick FAQ

Q: How do 「高さ」 vs 「高み」, 「甘さ」 vs 「甘み」 differ? Both turn adjectives into nouns.

The difference: 「さ」 marks an objective, measurable ‘degree,' 「み」 marks a subjective ‘sense/flavor/quality,' with feeling or state. 「〜さ」 = turns an adjective into a noun of ‘degree, measurement' (objective, neutral, often measurable): 高さは3メートル (the height is 3 meters — a measurable value); 甘さ控えめ (low sweetness — the objective degree of sweet); 難しさ (difficulty). It asks “how …,” a quantity concept. 「〜み」 = turns an adjective into a noun of ‘subjective feel, nuance, or state' (more literary, sensory): この曲には深みがある (this piece has depth/richness — the subjectively-felt “depth”); 甘みのあるスープ (a soup with sweetness — the felt “flavor, nuance” of sweet); 温かみのある人 (a person with warmth — human warmth). It's about “the sense, nuance, texture of …,” more qualitative, sensory. Compare: 「甘さ」 is the ‘degree' of sweet (adjustable high/low), 「甘み」 the ‘flavor, nuance' of sweet (with feeling). Also, 「さ」 attaches to nearly any adjective (高さ・低さ・美しさ…), while 「み」 attaches only to certain ones (深み・甘み・重み・痛み・温かみ, a limited set), not freely (×美しみ). Test: for objective measurement use さ, for subjective feel/nuance use み (and only on the idiomatic words).

Q: The prefixes 「不・無・非・未」 all negate — how do I choose?

They all negate but differ in feel and collocation, and are mostly fixed pairings (which word takes which prefix is conventional), with rough tendencies:

① 不〜 = not…, un- (bad) (‘lacking a good quality' or plain negation): 不便 (inconvenient); 不安 (uneasy); 不可能 (impossible); 不十分 (insufficient). The commonest negating prefix.

② 無〜 = without … (‘lacking, having none of something'): 無料 (free = no charge); 無理 (unreasonable = no logic); 無関係 (unrelated); 無意味 (meaningless). Stresses “none, lacking.”

③ 非〜 = non-…, not fitting … (‘not belonging to, not meeting a category/standard'): 非常識 (senseless = not fitting common sense); 非公開 (non-public); 非科学的 (unscientific); 非現実的 (unrealistic). Stresses “not fitting, not belonging.”

④ 未〜 = not yet … (‘not yet, incomplete,' with a temporal sense): 未完成 (unfinished); 未定 (undecided); 未成年 (a minor); 未解決 (unresolved). Stresses “not yet arrived.”

Roughly: 不 = not (good), 無 = without, 非 = not fitting/belonging, 未 = not yet. But which word takes which is fixed in practice (e.g., 「不可能」 not 「無可能」), so memorizing the prefix along with the word is safest; for a new word, use the tendencies above to guess the gist.

🖊️ Practice Questions (5)

Q1. 「不満」の「不」の役割は？

(A) 接尾辞 (suffix)

(B) 接頭辞 (prefix) indicating negation

(C) 複合語の前半

(D) 漢字の部首

Q2. What is the word-formation method of 「美しさ」?

(A) 接頭辞 + word

(B) word + 接尾辞 (〜さ)

(C) 名詞 + 名詞

(D) 動詞 + 動詞

Q3. 「書き込む」を分解すると？

(A) 書（書く）+ き込む

(B) 書き (the ます-form of 書く) + 込む (to enter)

(C) 書 + き + 込 + む

(D) 書き + こむ (a single native word)

Q4. 「音楽家」の「家」の意味は？

(A) house

(B) 家族

(C) 職業・専門家を表す接尾辞

(D) 漢字の部首

Q5. 「不思議」と「無関係」の「不」と「無」の共通点は？

(A) 完全に同じ意味

(B) どちらも否定の接頭辞 (prefix)

(C) 「不」は漢語、「無」は和語

(D) どちらも接尾辞

Answer Explanations

1. (B) 接頭辞 (prefix) indicating negation ── 「不満」(dissatisfaction) = 不 (negative prefix) + 満 (satisfaction). 「不〜」is a negative prefix of Sino-Japanese origin, placed before Sino-Japanese vocabulary to indicate negation: 不安・不満・不思議.

2. (B) word + 接尾辞 (〜さ) ── 「美しさ」(beauty) = 美しい (adjective) + さ (suffix: nominalization). 〜さ is a suffix that turns an adjective into a noun expressing degree/quality.

3. (B) ── 「書き込む」(to write in / fill in) = 書き (書く's ます-form with ます dropped) + 込む (the concept of entering). Compound verb: first verb's ます-form + second verb.

4. (C) ── 「音楽家」(musician) = 音楽 (music) + 家 (か). 〜家 (か) is a suffix meaning 'an expert/practitioner in a field': 作家・画家・評論家・政治家. It doesn't mean 'house/family.'

5. (B) ── 「不〜」and 「無〜」are both negative prefixes; they're close in meaning but their usage is conventional: 不満・不安・不思議 (不 + two-character Sino-Japanese word); 無条件・無関係・無理 (無 + two-character Sino-Japanese word). Which one to use is a fixed collocation that must be memorized.