Etymology: Two ablaut-forms in Old English: αþrýsce , later þryssce , weak feminine < Old Germanic *þrûskjôn . For the change of vowel in Middle English þrusche , thrush , compare clutch , crutch , rush , thrutch , with u /ʌ/ < y /y/; in 15th cent., some dialects retained þruysse (=þrüshe ) and thryshe , and thrice-cock (for thrȳshe-cock ) is still a dialect-name of the missel-thrush. βOld English had a800Anglian þrǽsce = West Saxon *þréasce = Old High German drôsca < Old Germanic *þrauskôn . Examples of this form are rare, and indeed not yet cited in Middle English, where it would be *þresche , *thresshe ; but thresh occurs in 17th cent., and the derivative thresher is dialectal in Oxfordshire. and Berkshire. Compare also the U.S. thrasher . There are also the derivative forms thrushel , thrishel , thrissel , from the α type: see thrushel n.

Etymology: Not known in either sense before the 17th cent., though the phonology of the word, with þ and sh , indicates English origin, and points to an Old English *þrusc . The only continental cognates appear to be, in sense 1, Swedish and Old Danish tørsk, Danish troske, Swedish dialect trosk, which Falk and Torp refer to an Old Norse *þruskr.Norwegian has frøsk , frosk ‘thrush’, phonetically identical with frosk frog; cf. Norwegian dialect trausk = frausk , ‘frog’, which seems to rest upon an old phonetic confusion of *þruskr and froskr . Some would connect this with the fact that Greek βάτραχος and Latin rāna , rānula , ‘frog’, were also names of a disease in the mouth of cattle. The evidence of English is however that *þrosc = Old Norse *þruskr , was the original word for the disease in sense 1. The connection of sense 2 is not explained; can it be connected with Danish trøske rotten or decayed wood, ‘rottenness in the bones’?