δοῦλον (doulon)

servant, slave; in the NT a person owned as a possession for various lengths of times (Hebrew slaves no more than seven years, Gentile slaves without time limit), of lower social status than free persons or masters; slaves could earn or purchase their freedom
a male slave, or servant, of various degrees, Mt. 8:9, and frequently ; a servitor, person of mean condition, Phil. 2:7; feminine δούλη, a female slave; a handmaiden, Lk. 1:38, 48; Acts 2:18; δοῦλος, used figuratively, in a bad sense, one involved in moral or spiritual thraldom, Jn. 8:34; Rom. 6:17, 20; 1Cor. 7:23; 2Pet. 2:19; in a good sense, a devoted servant or minister, Acts 16:17; Rom. 1:1; one pledged or bound to serve, 1Cor. 7:22; 2Cor. 4:5