thirl UK /θɜːl/US /θɝl/noun 5verb 5forms 3 noun5 •A hole, an aperture, especially a nostril. •(dialect) A low door in a dry-stone wall to allow sheep to pass through; a smoot. •(historical) A thrall. •(no longer used) A short communication between adits in a mine. •(no longer used) A long adit in a coalpit. verb5 •To pierce; to perforate, penetrate, cut through. •To bind; to obligate to use or be associated with.Was everyone nowadays thirled to a formula? — 1951 •(historical) To legally bind (a tenant) to the use of one's own property as an owner. •(no longer used) To drill or bore; to cut through, as a partition between one working and another. •(no longer used) To throw (a projectile). formsthirled · thirling · thirls