Fetching details from the dictionary...

suddenly; at once; in one go; with a jerk; with a gulp
considerably; very much; a lot
firmly; with an effort; tightly; exerting pressure
completely (e.g. at a loss)
deeply (e.g. moved)
彼女はぐっと唇を噛んで悔しさに耐えた。
She bit her lip hard and endured the frustration.
ぐっとこらえて何も言わずに我慢した。
I held back firmly and endured without saying anything.
感動してぐっと涙をこらえるしかなかった。
I was moved and could only hold back my tears.