Pulled or twisted suddenly with a quick, sharp movement, or made a sudden involuntary muscle contraction.
From Scottish 'jirk' meaning to pull or tug; possibly related to 'jerk' the dried meat, though the connection is debated; the word appeared in English by the 1600s.
Jerky movements of your arm when you're sleepy are called 'hypnic jerks'—they're evolutionary leftovers that mimicked our ancestors checking if they were about to fall out of trees.
Complete word intelligence in one call. Free tier — 50 lookups/day.