Definition of "foresail"

(nautical, on a square-rigged ship) The lowest (and usually the largest) square sail hung on the foremast  examples

(nautical) A square fore-and-aft sail set on the foremast, but behind it, on a schooner or other similar vessel.  examples

(nautical, on a sloop) A triangular sail set forward of the foremast: forestaysail.  examples