What is the meaning of grunt?

noun

• The short low gruff noise of the kind made by hogs.
  • synonyms: oink
• An unskilled or low-ranking soldier or other worker.
  • usage: "infantrymen in Vietnam were called grunts"; "he went from grunt to chairman in six years"
• Medium-sized tropical marine food fishes that utter grunting sounds when caught.

verb

• Issue a grunting, low, animal-like noise.
  • usage: "He grunted his reluctant approval"