asekha: (lit.: 'not-learner'; s. sekha), a disciple 'perfected in training', one beyond training, an adept. This is a name for the Arahat, the Holy One (s. ariya-puggala), since he has reached the perfection in higher moral training, higher mind training and higher wisdom training (s. sikkhā) and needs no longer to train himself therein.

Buddhist Dictionary, Manual of Buddhist Terms and Doctrines, by NYANATILOKA MAHATHERA

asekha : [adj.] one who does not require any further training. (m.) an Arahant.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]

Asekha (& Asekkha) (adj. n.) [a + sekha] not requiring to be trained, adept, perfect, m. one who is no longer a learner, an expert; very often meaning an Arahant (cp. B.Sk. aśaikṣa occurring only in phrase śaikṣâśaikṣāh those in training & the adepts, e.g. Divy 261, 337; Av. Ś i.269, 335; ii.144) Vin i.62 sq.; iii.24; S i.99; D iii.218, 219; It 51 (asekho sīlakkhandho; v. l. asekkha); Pug 14 (= arahant); Dhs 584, 1017, 1401; Kvu 303 sq.
   -- muni the perfectly Wise DhA iii.321. -- bala the power of an Arahant, enumd. in a set of 10 at Ps ii.173, cp. 176.

Pali-English Dictionary, TW Rhys Davids, William Stede,