ride a horse foaled by an acorn verb1 •(slang, no longer used) To be hanged on the gallows.You'll ride on a horse that was foal'd of an acron. That is; the gallows. — 1670 formsrid a horse foaled by an acorn · rode a horse foaled by an acorn · ridden a horse foaled by an acorn · riding a horse foaled by an acorn · rides a horse foaled by an acorn