From Longman Dictionary of Contemporary Englishwinnowwin‧now /ˈwɪnəʊ $ -noʊ/ (also winnow down) verb TA[transitive] to make a list, group, or quantity smaller by getting rid of the things that you do not need or want SYN whittle down We need to winnow the list of candidates to three. → winnow somebody/something ↔ out→ See Verb table
Examples from the Corpus
winnow• But in government, managers have no incentive to winnow out their product mix.• The Arizona primary was supposed to winnow the field of Republican presidential hopefuls.• Adams has winnowed the list of contestants to 12.• Again the problem is to winnow these down to manageable proportions.Origin winnow Old English windwian 