means A fine-grained gray rock that splits into flat sheets, historically used for roofing, writing tablets, and chalkboards — and, by extension, a list of candidates or scheduled items waiting to be approved.

from From Old French 'esclate,' a feminine form of 'esclat' meaning a splinter or fragment broken off — the same root that gives us 'slat.' The name fits the stone perfectly: slate is defined by how it cleaves into thin, splintered sheets. The political and scheduling sense ('a slate of candidates,' 'wipe the slate clean') comes from the slate writing-tablets once used to jot temporary lists, easily erased and started over.