disparage, belittle, pick at - express a negative opinion of; "She disparaged her student's efforts"

deflate, puncture - reduce or lessen the size or importance of; "The bad review of his work deflated his self-confidence"

devaluate, devalue, undervalue, depreciate - lose in value; "The dollar depreciated again"

write down, write off - reduce the estimated value of something; "For tax purposes you can write off the laser printer"

devalue - lower the value or quality of; "The tear devalues the painting"

decrease, diminish, lessen, fall - decrease in size, extent, or range; "The amount of homework decreased towards the end of the semester"; "The cabin pressure fell dramatically"; "her weight fall to under a hundred pounds"; "his voice fell to a whisper"

depreciate - lower the value of something; "The Fed depreciated the dollar once again"