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Webster 1913 Edition

Noun.

(Naut.)

(a)

The sail bent to the foreyard of a square-rigged vessel, being the lowest sail on the foremast.

(b)

The gaff sail set on the foremast of a schooner.

(c)

The fore staysail of a sloop, being the triangular sail next forward of the mast.

Noun.

A sail extended on the foreyard, which is supported by the foremast.

foresail ‎(plural foresails)

(nautical, on a square-rigged ship) The lowest (and usually the largest) square sail hung on the foremast
(nautical) A square fore-and-aft sail set on the foremast, but behind it, on a schooner or other similar vessel.
(nautical, on a sloop) A triangular sail set forward of the foremast: forestaysail.

lowest square sail on foremast

square fore-and-aft sail set behind the foremast

in a sloop: triangular sail attached to forestay