てっきり

adverb

surely; certainly (mistaken belief)

1. surely; certainly; definitely

Used when the speaker was confident about something that turned out to be wrong, or when expressing a strong assumption. Often implies the belief was mistaken.

てっきり彼(かれ)が来(く)ると思(おも)っていた。

I was sure he would come.

てっきり日本人(にほんじん)だと思(おも)ったら、韓国人(かんこくじん)だった。

I was certain they were Japanese, but they turned out to be Korean.

てっきり知(し)っているものだと思(おも)っていた。

I assumed you definitely knew about it.

Common patterns

てっきり is almost always used with past tense or assumptions that proved wrong. It expresses that the speaker was confident about something.

てっきり〜と思(おも)う - to be sure that ~
てっきり〜と思(おも)っていた - I was sure that ~
てっきり〜だと思(おも)ったら - I was sure it was ~, but then

Usage

Implies strong confidence that was potentially or actually mistaken. Often appears in sentences where the speaker's assumption turned out to be wrong.

Similar words

きっと - certainly (neutral, not implying mistake)
てっきり - certainly (often implies the assumption was wrong)

Related Words

Compare: きっと (certainly (neutral))

general

Added 2026.1.20 17:19 · Revised 2026.9.2 13:01

07500/07511_tekkiri