decrease, lessening, drop-off -- (a change downward; "there was a decrease in his temperature as the fever subsided"; "there was a sharp drop-off in sales")
decrease, decrement -- (a process of becoming smaller or shorter)
decrease, decrement -- (the amount by which something decreases)
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 fell to under a hundred pounds"; "his voice fell to a whisper")
decrease, lessen, minify -- (make smaller; "He decreased his staff")