Noun
errand; mission; going on an errand
使いの途中道草をくうな。Don't delay on this errand. messenger; bearer; errand boy; errand girl
familiar spirit
see 使い魔
Noun, used as a suffix, Noun, used as a prefix
use; usage; user; trainer; tamer; handler; charmer
Also written 遣い【つかい】