grubyoudaoicibaDictYouDict[grub 词源字典]
grub: [13] Grub ‘dig’ comes ultimately from prehistoric Germanic *grub-, perhaps via Old English *grybban, although no record of such a verb has actually come down to us (the related Germanic *grab- gave English grave, while a further variant *grōb- produced groove [15]). The relationship of grub ‘dig’ to the various noun uses of the word is far from clear. Grub ‘larva’, first recorded in the 15th century, may have been inspired by the notion of larvae digging their way through wood or earth, but equally it could be connected (via the idea of ‘smallness’) with the contemporary but now obsolete grub ‘short, dwarfish fellow’ – an entirely mysterious word. Grub ‘food’, which dates from the 17th century, is usually said to have been suggested by birds’ partiality for grubs or larvae as part of their diet.

And in the 19th century a grub was also a ‘dirty child’ – perhaps originally one who got dirty by digging or grubbing around in the earth – which may have been the source of grubby ‘dirty’ [19].
=> grave, groove[grub etymology, grub origin, 英语词源]
grub (v.)youdaoicibaDictYouDict
c. 1300, "dig in the ground," from hypothetical Old English *grybban, *grubbian, from West Germanic *grubbjan (cognates: Middle Dutch grobben, Old High German grubilon "to dig, search," German grübeln "to meditate, ponder"), from PIE *ghrebh- (2) "to dig, bury, scratch" (see grave (n.)). Transitive sense "dig up by the roots" is from 1550s. Related: Grubbed; grubbing.
grub (n.)youdaoicibaDictYouDict
"larva of an insect," early 15c., perhaps from grub (v.) on the notion of "digging insect," or from the possibly unrelated Middle English grub "dwarfish fellow" (c. 1400). Meaning "dull drudge" is 1650s. The slang sense of "food" is first recorded 1650s, said to be from birds eating grubs, but also often linked with bub "drink."