とうとう

と

う

と

う

Meanings

1

usually written using kana alone

Expresses that something happens after a long time, effort, or process, often with a sense of inevitability or culmination.

長なが

い

冬ふゆ

が

終お

わり

、

とうとう

春はる

が

来き

た

。

The long winter ended, and spring finally came.

彼かれは何なん度ども挑ちょう戦せんして、とうとう夢ゆめをかなえた。

He tried many times and at last achieved his dream.

とうとう〜てしまうfinally ended up doing (something), often with regret or resignation
彼かれはとうとう会かい社しゃを辞やめてしまった。
In the end, he finally quit the company.
とうとう〜なかったin the end, (something) never happened
彼かの女じょはとうとう戻もどってこなかった。
In the end, she never came back.
とうとう〜になるfinally reached a certain state or point
長ながい交こう渉しょうの末すえ、とうとう合ごう意いに達たっした。
After long negotiations, they finally reached an agreement.

やっとN4
やっと stresses relief after effort or waiting, while 到頭 can also convey inevitability, sometimes with a negative nuance.
ついにN3
ついに is close in meaning to 到頭 but tends to sound more formal or dramatic; the two are often interchangeable.
結けっ局きょくN3
結局 means "in the end/after all" and focuses on the final outcome, whereas 到頭 emphasizes the long process leading up to that moment.

とうていN1
到頭（とうとう, 'finally, at last') shares the kanji 到 with 到底（とうてい, 'not possibly') but has a completely unrelated meaning.

とうとうUsage99%
Standard kana spelling; the word is usually written in kana.
到とう頭とうUsage1%
rarely-used kanji form
Rarely used kanji form; learners should use the kana spelling.
トウトウUsage<1%

The historical derivation is uncertain; the kanji 到頭 (arrive + head) are ateji used for their sound, not their meaning.