How to say "profoundly" in Japanese

• ずっしり
  adverb (with と), suru verbA mimetic word whose basic sense is 'heavily': it evokes physical weight and, by extension, a weighty, substantial quality. Its 'profoundly' is only that extension, seldom depth of thought or emotion.
• ずしっと
  adverb, suru verbLike ずっしり, this mimetic word works through 'heavily': its 'profoundly' means a heavy, weighty quality rather than genuine profundity. For deep thought or feeling it is rarely the word you want.
  この箱ばこ、持ち上もちあげるとズシッと重おもいね。中なかに何なんが入はいってるんだ。↗

  This box weighs a ton. What's inside?
• つらつら
  adverb (with と)Its 'profoundly' belongs to thought: it describes pondering or considering something carefully, closely and attentively, and is normally written in kana. Use it for deep, deliberate reflection rather than emotional depth.
• 深くふかく
  adverbThe straightforward adverb of depth: use it for 'profoundly' in emotional and evaluative senses — being deeply moved, affected or convinced. Its other senses, 'intimately', 'heartily' and 'sincerely', make it the most broadly applicable choice.
  その小説しょうせつを読よんで深ふかく感動かんどうした。↗

  I was deeply moved by that novel.

Choose 「深く」 for depth of feeling or degree and 「つらつら」 for deep, careful thought; 「ずっしり」 and 「ずしっと」 are weight mimetics whose 'profoundly' is really 'heavily', describing weighty substance rather than profundity.

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

• ずっしりheavily
• ずしっとheavily
• つらつらcarefully
• 深くふかくdeeply
• ジーンと(being moved) deeply