1. suddenly; at once; in one go; with a jerk; with a gulp
二人は再び、ジュースをぐっと飲み干した。The two of them again downed their juice in one gulp.
2. considerably; very much; a lot
3. firmly; with an effort; tightly; exerting pressure
でも、その衝動をぐっと我慢します。But I firmly hold back that impulse.
4. completely (e.g. at a loss)
5. deeply (e.g. moved)
その言葉が、心にぐっと深く刺さった。Those words pierced deeply into my heart.