grunt
v.
Old English grunnettan "to grunt," frequentative of grunian "to grunt," probably imitative (compare Danish grynte, Old High German grunnizon, German grunzen "to grunt," Latin grunnire "to grunt"). Related: Grunted; grunting.
n.
1550s, from grunt, v.; as a type of fish, from 1713; meaning "infantry soldier" emerged in U.S. military slang during Vietnam War (first recorded in print 1969); used since 1900 of various low-level workers. Grunt work first recorded 1977.