gag (v.) Look up gag at Dictionary.com
mid-15c., transitive, "to choke, strangle" (someone), possibly imitative and perhaps influenced by Old Norse gag-hals "with head thrown back." The sense of "stop a person's mouth by thrusting something into it" is first attested c.1500. Intransitive sense of "to retch" is from 1707. Transitive meaning "cause to heave with nausea" is from 1945. Related: Gagged; gagging.
gag (n.2) Look up gag at Dictionary.com
"a joke," 1863, especially a practical joke, probably related to theatrical sense of "matter interpolated in a written piece by the actor" (1847); or from the sense "made-up story" (1805); or from slang verbal sense of "to deceive, take in with talk" (1777), all of which perhaps are from gag (v.) on the notion of "to stuff, fill" (see gag (v.)). Gagster "comedian" is by 1932.
gag (n.1) Look up gag at Dictionary.com
"something thrust into the mouth or throat to prevent speaking," 1550s, from gag (v.); figurative use, "violent or authoritative repression of speech," is from 1620s.