(1):

(v. t.) To injure by working secretly; to destroy or overthrow by clandestine measure; to undermine.

(2):

(v. t.) To do like work at a less price than; as, one mason may underwork another.

(3):

(v. i.) To do less work than is proper or suitable.

(4):

(v. t.) To expend too little work upon; as, to underwork a painting.

(5):

(v. i.) To do work for a less price than current rates.

(6):

(v. i.) To work or operate in secret or clandestinely.

(7):

(n.) Inferior or subordinate work; petty business.