adverb, noun which may take the genitive case particle 'no', na-adjective
very; greatly; considerably; quite
Emphasizes a high degree or extent, often with a nuance of 'more than usual' or 'to a surprising degree'. Used adverbially or with の/な to modify nouns.
See also:
今日はよっぽど疲れたみたいだね。
You seem really tired today.
よっぽどのことがない限り、彼は遅刻しない。
Unless something very unusual happens, he won't be late.
almost; very nearly; just about to
Indicates that something was close to happening or being the case, often with a sense of 'to a considerable degree' that almost reached a threshold. Used adverbially.
See also: よほど
よっぽど言おうかと思ったけど、やめた。
I almost said it, but I stopped myself.
Unless something really out of the ordinary happens, he won't break his promise.
I was almost about to go home, but I changed my mind.
He must be really tired, since he's been sleeping this whole time.
Unless there's a really compelling reason, he won't be late.