c.1300, from hypothetical O.E.
*grubbian, from W.Gmc.
*grubbjan (cf. O.H.G.
grubilon "to dig, search," Ger.
grübeln "to meditate, ponder"), from P.Gmc.
*grub- "to dig," base of O.E.
grafan (see
grave (v.)). The noun sense of "larva" (c.1400) is perhaps from the notion of "digging insect," or from the possibly unrelated M.E.
grub "dwarfish fellow." The slang sense of "food" is first recorded 1659, said to be from birds eating grubs, but also often linked with
bub "drink."
Grubby is c.1845, from
grub (n.) in a sense of "dirty child," who presumably got that way from digging in earth.
[gruhb] 
noun, verb, grubbed, grub⋅bing.
