Webster's English Dictionary

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thyroid

1. thy.roid \'thi-(*)r-.o.id\ aj [NL thyroides, fr. Gk thyreoeide-s 
   shield-shaped, thyroid, fr. (Xthyreos shield shaped like a door, fr. thyra 
   door - more at DOOR 1a: of, relating to, or being a large endocrine of 
   craniate vertebrates ly ing at the base of the neck and producing an 
   iodine-containing hormone that affects esp. growth, development, and 
   metabolic rate 1b: suggestive of a disordered thyroid {a ~ personality}  2: 
   of, relating to, or being the chief cartilage of the larynx 
2. thyroid n 1: a thyroid gland or cartilage; also : a part (as an artery 
   or ner ve) associated with either of these 2: a preparation of mammalian 
   thyroid gland used in treating thyroid disord ers