How to say "cap" in Japanese

• キャップCommon
  nounThe headwear sense: the specific word for a cap, typically the peaked, baseball-style kind, as opposed to headwear in general. Use it when English 'cap' means that particular type of hat.
• 蓋ふたJLPT N2approx.Common
  nounThe closure sense: a lid or cover fitted over the opening of a bottle, jar, or similar container. When 'cap' means the removable top of something, this is the word.
  このふたはあのジャーのふただ。↗

  This lid belongs with that jar.
• ぼうしJLPT N5approx.Common
  nounThe general word for headwear, covering both hats and caps. When 'cap' just means headwear and no particular style is intended, this is the word to use.
  この帽子ぼうしは１０００円えんなら安やすい。↗

  This hat is cheap at 1000 yen.
• 頭巾ずきんCommon
  nounEssentially a hood or kerchief: cloth headgear worn over the head. For an ordinary cap this is only marginally relevant — it is seldom the word you want.
  修道士しゅうどうしのように頭巾ずきんをかぶった雲くもは、ポツリポツリと落おちる雨あめを数珠じゅずのようにつまぐっている。↗

  The hooded clouds, like friars, tell their beads in drops of rain.
• さやCommon
  nounThe cap fitted on a pen, brush, or similar item; the same word also means 'case' and 'sleeve'. It is usually written in kana alone.

For headwear, 「キャップ」 is the specific cap and 「ぼうし」 the general word; 蓋 covers lids and container caps, 「さや」 the cap on a pen or brush, while 頭巾 is really for hoods and other cloth headgear.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• キャップcap (hat)
• 蓋ふたcover
• ぼうしhat
• 頭巾ずきんheadgear (esp. one made of cloth)
• 帽ぼうhat
• 競合アクセス業者きょうごうアクセスぎょうしゃCAP
• 冠するかんするto crown
• かぶせ物かぶせもの(dental) crown
• 冠すかんすto crown
• 上蓋うわぶたlid (of a box, container, etc.)
• 直掩ちょくえんdirect escort
• 口金くちがね(metal) cap
• キャスケット(largish) cap
• 鳥打帽とりうちぼうflat cap
• さやcap (on a brush, pen, etc.)