the very end; the finish
Used as a noun to refer to the absolute end or limit of something, often in set phrases like とことんまで.
とことんまで話し合おう。
Let's talk it out to the very end.
The two of them talked things through thoroughly.
Adverbial use meaning doing something exhaustively, without giving up, or to the fullest extent.
彼はとことん調べてから結論を出した。
He investigated thoroughly before reaching a conclusion.
とことん楽しんでください。
Please enjoy yourself to the fullest.
彼はとことんまで諦めなかった。
He never gave up, all the way to the end.
I stuck with my friend's problem all the way through.
存分に means doing something as much as one likes or is satisfied with, while とことん implies pushing on to an absolute limit even against difficulty.
とことん is a colloquial word for doing something thoroughly or to the extreme, while あくまでも stresses a persistent, unwavering stance and sounds a bit more formal.
とことん is a colloquial way to say 'thoroughly, all the way' (as in とことんやる), while あくまで can add a stubborn or insistent nuance.
Kana-only mimetic word; no kanji spelling is given.
A mimetic word of uncertain origin, possibly related to the reduplicated sound-symbolic pattern とんとん or ことん, but the exact derivation is unclear.