ぐっと
ぐっと · gutto · JLPT N1 · noun
firmly
✊ ぐっ = sound of a sudden clench; ぐっと = clenching hard, so firmly, fast, or a sharp jump up
ぐっ mimics a sudden grip or push, and adding と makes it an adverb. A tight grip means firmly, a sudden push means fast, and a sudden step up means more.