(figuratively) A cue, warning, or alert; a sign or signal that something is wrong. / (idiomatic, US) red rag

(literary) Guilty of terrible crimes; wicked, criminal. / (literary) Extremely brutal or wicked; heinous, monstrous.

a large blowlamp used to control weeds etc.

A perennial wetland plant, Acorus calamus, with an aromatic medicinal root, formerly used to strew floors.

The act of burning a flag, especially the flag of a nation as an act of protest at that nation's activities.

(biology) In protists, a long, whiplike membrane-enclosed organelle used for locomotion or feeding. / (biology) In bacteria, a long, whiplike proteinaceous appendage, used for locomotion. / A whip

plural of flagellum

(motor racing) A black-and-white chequered flag which signifies the end of a race. / (motor racing) A victory in a race.

(intransitive) To wave one's arms (or upper body) about violently, rather like a flail.

(transitive) To whip or scourge. / (transitive) Of a spermatozoon, to move its tail back and forth.