also: がぷっと
adverb
chomping; gulping; with a big bite
Mimetic adverb describing the sound or action of biting or swallowing something vigorously, often in one large mouthful.
犬が大きな肉をガブッとくわえた。
The dog chomped down on a big piece of meat.
彼はハンバーガーをガブッと一口で食べた。
He gulped down the hamburger in one big bite.
がつがつ describes eating greedily or ravenously over a period, whereas ガブッと focuses on a single vigorous bite or gulp.
Onomatopoeic formation from the sound of a forceful bite or gulp. The exact origin is uncertain.