From Old English 'styrian' (to move, agitate), from PIE *twer- (to turn) — the cooking sense is a narrowing of 'to agitate.'
To move a spoon or other implement around in a liquid; to move slightly or begin to be active.
From Old English 'styrian' meaning 'to move, agitate, disturb,' from Proto-Germanic *sturjaną (to stir up, disturb), from PIE *twer- (to turn, whirl). The cooking sense is a specific application of the general meaning 'to agitate.' Key roots: *twer- (PIE: "to turn, whirl").