belchyoudaoicibaDictYouDict[belch 词源字典]
belch: [OE] Belch first appears in recognizable form in the 15th century, but it can scarcely not be related to belk ‘eructate’, which goes back to Old English bealcan and survived dialectally into the modern English period. Belch itself may derive either from an unrecorded variant of bealcan, *belcan (with the c here representing a /ch/ sound), or from a related Old English verb belcettan ‘eructate’.

But whichever route it took, its ultimate source was probably a Germanic base *balk-or *belk-, from which German got bölken ‘bleat, low, belch’. Belch was originally a perfectly inoffensive word; it does not seem to have been until the 17th century that its associations began to drag it down towards vulgarity.
[belch etymology, belch origin, 英语词源]
belch (v.)youdaoicibaDictYouDict
Old English bealcan "bring up wind from the stomach," also "swell, heave," of echoic origin (cognates: Dutch balken "to bray, shout"). Extended to volcanoes, cannons, etc. 1570s. Related: Belched; belching. As a noun, recorded from 1510s. It is recorded in 1706 as a slang noun meaning "poor beer."