a great deal; very much; a lot
Emphatic adverb used to stress a large amount or degree, often in casual speech. Common with verbs like 食べる, 勉強する, or adjectives.
I slept a lot yesterday.
I studied very hard and passed the exam.
with great effort
Archaic use emphasizing strenuous effort. Rare in modern Japanese; replaced by expressions like 一生懸命 or 精一杯.
In classical texts, it was used like 'to strive with great effort'.
I want to play a lot during summer vacation.
This watermelon is much bigger than last year's.
You're at a growing age, so eat a lot.
I plan to study very hard for next year's exam.
いっぱい is a casual word meaning 'full' or 'a lot', close in feel to うんと but without うんと's extra emphasis on degree.
Kana adverbial form; no kanji spelling is given.
Onomatopoeic or mimetic origin, likely from the sound of forceful exhalation or effort. The exact derivation is uncertain.