An onomatopoeic/mimetic expression describing a sudden start or a sharp, startled movement; often used adverbially or in compounds.
背後から声をかけられて、ぎっくり振り向いた。
Someone called from behind, and I turned around with a start.
夜中に物音がして、彼はぎっくりベッドから飛び起きた。
A noise in the middle of the night made him jump out of bed with a start.
先生の突然の質問に、学生たちはぎっくりと表情を強ばらせた。
At the teacher's sudden question, the students' expressions stiffened in surprise.