grub

First recorded in 1250–1300; Middle English grubbe (noun), grubben (verb); akin to Old High German grubilōn “to dig,” German grübeln “to rack (the brain),” Old Norse gryfia “hole, pit”; see grave¹, groove

The English noun grub, first recorded in the 15th century with the meaning “larva of an insect,” derives from the verb. The Middle English verb grubben, grobben “to dig the earth (with a tool)” comes from an unrecorded Old English verb grybban, grubbian and is akin to Gothic graban “to dig,” Old High German grubilōn “to dig, search for,” Middle Dutch grobben, and Dutch grobbelen “to root about, feel about for something.”
The Germanic words all derive from the Germanic root grab- “to dig, bury, scratch,” source of the English noun grave “excavation in the earth for burial of a body” and the verb grave “to carve or sculpt.”
The “food, victuals” slang meaning of grub dates from the mid-17th century. The slang meaning “to beg or scrounge” dates from the late 19th century.