sift. 1  to separate and retain the coarse parts of (flour, ashes, etc.) with a sieve. 2  to scatter or sprinkle through or by means of a sieve: to sift sugar onto cake. 3  to separate by or as if by a sieve. 4  to examine closely: The detectives are still sifting the evidence. 5  to question closely. 6  to sift something.