The thyroid was a gland found in the endocrine system of many species, which regulated hormones in the body. Among the systems affected by the thyroid gland were those regulating body size.
In Takarans, the thyroid gland was located in the lateral sternal. (TNG: "Suspicions")
In 2267, to snap Spock out of his Omicron spore-induced spell, James T. Kirk taunted him by calling him, among other things, "an elf with a hyperactive thyroid" (TOS: "This Side of Paradise")
In 2371, after noting rapid cell division in a Jem'Hadar baby Quark had unknowingly taken possession of, Doctor Julian Bashir's examination found no thyroid or hypothalamus issues that would explain it. (DS9: "The Abandoned")
In 3188, Cleveland Booker told Michael Burnham that Grudge had a thyroid condition. (DIS: "That Hope Is You, Part 1")
In a deleted scene from ENT: "Minefield", the phrase for the thyroid gland is said to be "y'sah mai-kaam" in the Denobulan language. Phlox mentions this while testing Hoshi Sato's Denobulan while she was recovering after being injured by a Romulan mine in 2152.