最初|さいしょsaisho[0]heiban (flat)

1. no-adjective, adverbbeginning; outset; first; onset
   その考かんがえは最初さいしょのうちはばかげているように思おもえた。↗

   The idea seemed absurd at first.

• SynonymはじめNeutralNeutral and broader in use than 「最初」: it covers the opening part of something and also the act of starting to do it.
• Synonym始まりはじまりNeutralNeutral noun for the moment something starts or the origin of a thing — 「物語の始まり」. It names the start itself, not first place in an order.
• Synonym冒頭ぼうとうWrittenWritten/formal prose. The opening of a text, speech, film or meeting — 「会議の冒頭」. 「最初」 is the general word for whatever comes first in order.
• Synonym幕開けまくあけWrittenWritten/formal prose. The grand opening of a new era or an event, with a ceremonial ring — 「新時代の幕開け」. Far more elevated than plain 「最初」.
• Synonym振り出しふりだしCasualColloquial. A starting point, used mostly in 「振り出しに戻る」 — back to square one, everything starting over.
• SynonymスタートCasualColloquial loanword for a start, especially in races — 「スタートを切る」. 「最初」 is the plain word for first in order.
• SynonymはじめにNeutralNeutral phrase: first of all, at the very beginning; also the heading of a book's preface or introduction.
• SynonymまずNeutralNeutral adverb meaning first or to begin with, as in 「まず手を洗う」 — it orders actions rather than naming the start.
• Synonym当初とうしょWrittenWritten/formal prose. At first, initially — looking back from later on, often in contrast with what followed: 「当初の予定」.
• Synonym原初げんしょWrittenWritten/formal prose. The most primordial origin of things — 「原初の世界」. Far weightier than 「最初」, and only for origins, not everyday firsts.
• Synonym出だしでだしCasualColloquial word for the opening of an event or a song, with an eye on how it goes, as in 「出だしは好調」. Focuses on the way things start, not just position in a sequence.
• Synonym序開きじょびらきWrittenWritten/formal prose for the very start of something; extremely rare — say 「始め」 in everyday speech.
• SynonymしょっぱなCasualColloquial and emphatic: right at the very start, often with something happening immediately — 「初っ端から失敗した」.
• Synonym初発しょはつWrittenWritten/formal prose. The first departure of the day, as in 「初発電車」, or the earliest occurrence of something — much narrower than 「最初」.
• Synonymとば口とばくちCasualColloquial. An entrance or threshold, or the stage where something has just begun — 「研究のとば口」. Not about first position in a sequence.
• SynonymビギニングCasualLoanword for a beginning, seen mostly in the titles of works; not part of everyday speech.
• SynonymとっつきCasualColloquial. The stage where something has just begun, or the first thing you run into — 「取っ付きの部屋」. 「最初」 is the general word for first in order.
• Related発端ほったんWrittenWritten/formal prose. The origin of an incident, used when recounting how it came about — 「事件の発端」. 「最初」 just marks the first point in order.
• Related滑り出しすべりだしCasualColloquial. How something goes right after it starts — 「滑り出しは順調」. Judges whether the start is smooth, where 「最初」 simply points to the first stage.
• Related出始めではじめCasualColloquial. The time when seasonal goods first appear on the market — 「出始めの野菜」. Limited to things coming out; 「最初」 is general.
• Antonym最後さいごNeutralAntonym. The last in order, the opposite end of a sequence from 「最初」.
• Antonym終わりおわりNeutralAntonym. The end or winding-up stage of something, opposed to 「最初」.

Default to 「最初」 for whatever comes first in order. Use 「始め」 for the opening part of something, 「出だし」 or 「滑り出し」 for how a start goes, 「冒頭」 for the opening of a text, speech or meeting, 「まず」 for 'first, do X', and 「当初」 for 'at first, but later…'. 「発端」 and 「原初」 are for origins, 「幕開け」 for grand new beginnings, 「振り出しに戻る」 for starting over. Opposites: 「最後」, 「終わり」.

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

1. 最もっとも初はじめ。物事ものごとの始はじまり。