An autoantonym is a word which has two meanings which are opposites of each other. It may have several other meanings - only the two contradictory meanings are significant and give an autoantonym its curious "Humpty-Dumpty" quality.

The word cleave - meaning either 'to split asunder' or 'to join together' - is a perfect example of an autoantonym.

DUSTremove dustsprinkle with dust
INFLAMMABLEflammablenot flammable
INHABITABLEhabitablenot habitable
INSCIENTignoranthaving secret or inward knowledge
LEFTremaininggone away
LETto permitto hinder, to prevent
PINKa light red coloura greenish-yellow pigment
QUITEcompletely, absolutelyto a partial extent, somewhat
ROCKa sure foundation, anything immovablea swaying or tilting movement
SCREENto conceal from viewto display (a film etc.)
TRIPto move lightly and nimblyto stumble
VAPULATEto flogto be flogged