再三|さいさんsaisan[0]heiban (flat)

1. adverb, no-adjectiveagain and again; repeatedly
   彼かれは私に、再三さいさん電話でんわをかけてきた。↗

   He telephoned me again and again.

• SynonymたびたびNeutralMeans often or repeatedly, focusing on the sheer number of times; 「再三」 stresses one thing happening over and over, as in repeated warnings, requests or breakdowns.
• SynonymしばしばWrittenSame word as above: written in flavor, meaning often, repeatedly; 「再三」 stresses one thing repeated, as in warnings or accidents.
• Synonym再々さいさいWrittenClose to 「再三」 in meaning — again and again, time after time — but used far less often.
• SynonymちょくちょくCasualColloquial; means now and then, every few days or so; 「再三」 is the more formal choice.
• Synonym繰り返しくりかえしNeutralMeans repetition — the same thing done over and over in a cycle; 「再三」 stresses many times over, again and again.
• Synonym重ね重ねかさねがさねWrittenWritten and formal; means repeatedly and wholeheartedly, used chiefly in expressing thanks or apologies, as in 「重ね重ねお礼申し上げます」.
• Synonym再三再四さいさんさいしWrittenA four-character compound meaning again and again, stressing just how many times something happens.
• RelatedちょいちょいCasualColloquial and light in tone; means often or frequently.
• RelatedしょっちゅうCasualColloquial; means all the time, constantly; 「再三」 leans formal.
• RelatedしきりにNeutralMeans incessantly, one thing after another, and can also suggest eagerness; 「再三」 centers on the number of times.
• Related往々おうおうWrittenWritten; means often, as things tend to go — it stresses a tendency, while 「再三」 stresses the number of times.
• Related時々ときどきNeutralMeans sometimes, occasionally — a lower frequency than 「再三」.
• Related頻繁ひんぱんNeutralA na-adjective meaning frequent, as in 「頻繁に起こる」.
• Related始終しじゅうNeutralMeans from start to finish, all along — it stresses continuity, while 「再三」 stresses the number of times.
• Related間々ままWrittenWritten; means occasionally, now and then — a lower frequency than 「再三」.
• Related幾重にもいくえにもWrittenWritten; means over and over, layer upon layer, used mainly in earnest pleas or apologies.
• Related返す返すかえすがえすWrittenMeans deeply, intensely — used mostly to voice regret, as in 「返す返すも残念」.
• Related一度ならずいちどならずNeutralMeans more than once, not just a single time; plainer in tone than 「再三」.
• Antonym一度いちどNeutralMeans once, a single time — the opposite of 「再三」's repeated many times.
• Antonym一回いっかいNeutralMeans once, one round or one game — the opposite of 「再三」.

Use 「再三」 for doing something over and over, as in 「再三注意した」 or 「再三の故障」. When something simply happens often, 「度々」 or 「しばしば」 is the natural pick, and 「頻繁」 for high frequency. For thanks or apologies, 「重ね重ね」 is the word. For a single occurrence, say 「一度」. In casual speech, 「ちょくちょく」 and 「しょっちゅう」 stand in for the formal 「再三」.

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

1. 二に度ども三さん度ども。何度なんども。