The Collaborative International Dictionary of English v.0.48:

Mistreat \Mis*treat"\, v. t.
   To treat amiss; to abuse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mistreat
    v 1: treat badly; "This boss abuses his workers"; "She is always
         stepping on others to get ahead" [syn: mistreat,
         maltreat, abuse, ill-use, step, ill-treat]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "mistreat":
   abuse, afflict, aggrieve, batter, befoul, bewitch, blight, bruise,
   brutalize, buffet, condemn, corrupt, crucify, curse, damage,
   defile, deprave, despoil, destroy, disadvantage, disserve,
   distress, do a mischief, do evil, do ill, do violence to, do wrong,
   do wrong by, do wrong to, doom, envenom, get into trouble, harass,
   harm, hex, hurt, ill-treat, ill-use, impair, infect, injure, jinx,
   knock about, maltreat, manhandle, maul, menace, mishandle, misuse,
   molest, outrage, persecute, play havoc with, play hob with, poison,
   pollute, prejudice, rough, rough up, savage, scathe, taint,
   threaten, torment, torture, violate, wound, wreak havoc on,
   wrong