Winnow down is a phrasal verb that means to reduce or narrow down the options to the best ones. It's commonly used when sorting through a list of items or ideas. There are many synonyms for winnow down, including sift, filter, weed out, cull, sort out, eliminate, and narrow. Each of these words describes the process of carefully examining and selecting the best options while discarding the rest. Sifting implies a thorough examination of many options, while filtering and weeding out suggest a focus on removing undesirables. Culling and elimination suggest a more drastic approach to reducing options. Whichever synonym is used, the ultimate goal of winnowing down is to arrive at a smaller, more manageable set of viable options.