thresholdyoudaoicibaDictYouDict[threshold 词源字典]
threshold: [OE] The first element of threshold is identical with English thresh [OE]. This seems to go back ultimately to a prehistoric source that denoted ‘making noise’ (the apparently related Old Church Slavonic tresku meant ‘crash’, and Lithuanian has trešketi ‘crack, rattle’). By the time it reached Germanic, as *thresk-, it was probably being used for ‘stamp the feet noisily’, and it is this secondary notion of ‘stamping’ or ‘treading’ that lies behind threshold – as being something you ‘tread’ on as you go through a door. Thresh by the time it reached English had specialized further still, to mean ‘separate grains from husks by stamping’, and this later evolved to simply ‘separate grains from husks’. Thrash [OE], which originated as a variant of thresh, has taken the further semantic step to ‘beat, hit’.

It is not known where the second element of threshold came from.
=> thrash, thresh[threshold etymology, threshold origin, 英语词源]
threshold (n.)youdaoicibaDictYouDict
Old English þrescold, þærscwold, þerxold, etc., "door-sill, point of entering," of uncertain origin and probably much altered by folk-etymology. The first element probably is related to Old English þrescan (see thresh), either in its current sense of "thresh" or with its original sense of "tread, trample." Second element has been much transformed in all the Germanic languages, suggesting its literal sense was lost even in ancient times. In English it probably has been altered to conform to hold. Liberman (Oxford University Press blog, Feb. 11, 2015) revives an old theory that the second element is the Proto-Germanic instrumental suffix *-thlo and the original sense of threshold was a threshing area adjacent to the living area of a house. Cognates include Old Norse þreskjoldr, Swedish tröskel, Old High German driscufli, German dialectal drischaufel. Figurative use was in Old English.