Translation guide
The English word "fast" covers speed, firmness, and abstinence. This guide helps learners choose the right Japanese expression for each meaning.
Describing something that moves or happens at high speed.
The most common adjective for speed. Use for vehicles, animals, actions, etc.
この車はとても速い。
This car is very fast.
彼は走るのが速い。
He runs fast.
Means 'early' or 'quick' in terms of time. Often used for prompt actions or early completion.
Do not use 早い for physical speed; use 速い instead.
Means 'nimble' or 'swift', often implying agility.
猫の動きは素早い。
The cat's movements are fast.
A noun or na-adjective meaning 'rapid', often used in formal or technical contexts.
急速な発展
rapid development
Describing something that is tightly fixed, stuck, or not easily moved.
Means 'firm', 'solid', or 'tight'. Used for objects, knots, handshakes, etc.
このネジはしっかりしている。
This screw is fast (tight).
しっかりと結んでください。
Please tie it fast (tightly).
Means 'hard' or 'firm'. Can describe a tight grip or a solid object.
彼は固い握手をする。
He gives a firm handshake.
Means 'immovable' or 'not budging', used for something firmly fixed.
その岩はびくともしなかった。
The rock was fast (didn't budge).
Abstaining from food, often for religious or health reasons.
The noun for 'fasting'. The verb is 断食する.
彼は宗教的な理由で断食をしている。
He is fasting for religious reasons.
Simply means 'not eat'. Use in casual contexts.
今日は何も食べない。
I'm fasting today (not eating anything).
Describing colors or dyes that do not run or fade.
Means 'color does not come off'. Common for clothing labels.
このシャツは色落ちしません。
This shirt is colorfast.
Means 'does not fade'. Used for long-lasting colors.
このカーテンは色あせしにくい。
These curtains are fast (fade-resistant).
Sleeping deeply.
Means 'sleeping soundly'. The adverb ぐっすり indicates deep sleep.
彼はぐっすり眠っている。
He is fast asleep.
Means 'in a deep sleep'. More formal than ぐっすり.
彼女は熟睡している。
She is fast asleep.
A close, loyal friend.
Both are read はやい. 速い is for physical speed (fast car, fast runner). 早い is for time-related quickness (early morning, prompt reply). Using the wrong kanji can confuse the meaning.
English 'fast' in 'fast asleep' does not mean speed. Do not use 速い or 早い. Use ぐっすり or 熟睡.