Synonyms and related words :
be at sea, be lost, belittle, de-emphasize, deprecate, depreciate, disparage, downplay, give up, make light of, make little of, minimize, misestimate, misprize, not understand, pass, play down, sell short, set at naught, set little by, shrug off, think little of, think nothing of, underestimate, underplay, underprize, underrate, underreckon, undervalue