Third-person singular simple present indicative form of mail it in

(historical) A bonus or gift given by an employer to an employee, by a master/mistress to his/her servants, or by a householder to delivery persons at Christmas time, traditionally on Boxing Day.

Consisting of, or relating to, two morphemes.

Vast in quantity or number, profuse, abundant; taking place on a large scale. / Having an abundant supply. / Full of thought, information, or matter; exuberant in words, expression, or style.