Asekha: lit.: Learned = not-anymore-learner see: sekha, a disciple perfected in training, one beyond training, an adept. This is a name for the Arahant, the Noble One see: ariya-puggala, since he has reached the perfection in higher moral training, higher mental training and higher understanding see: sikkhā and needs no longer to train himself therein.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.