Old English leornian "to get knowledge, be cultivated; study, read, think about," from Proto-Germanic *lisnojanan (cognates: Old Frisian lernia, Middle Dutch leeren, Dutch leren, Old High German lernen, German lernen "to learn," Gothic lais "I know"), with a base sense of "to follow or find the track," from PIE root *lois- "furrow, track." It is related to German Gleis "track," and to Old English læst "sole of the foot" (see last (n.1)).

From c. 1200 as "to hear of, ascertain." Transitive use (He learned me (how) to read), now considered vulgar (except in reflexive expressions, I learn English), was acceptable from c. 1200 until early 19c. It is preserved in past-participle adjective learned "having knowledge gained by study." Old English also had læran "to teach" (see lere). Related: Learning.

1620s, from learn + -able. Related: Learnability.

occasional past tense and past participle of learn.

mid-15c., from un- (2) "reverse, opposite of" + learn (v.).

1865, from German Lehrjahre, from lehren "to learn" (see learn) + Jahre "years" (see year (n.)).

c. 1400, "ignorant," from un- (1) "not" + learned (adj.). From 1530s as "not acquired by learning," from past participle of learn (v.). Old English had unlæred.

"having knowledge gained by study," mid-14c., past-participle adjective from learn (v.) in its former transitive sense. Related: Learnedly; learnedness. "[L]earned expresses depth and fullness in the knowledge, while scholarly expresses accuracy" [Century Dictionary].

Old English leornung "study, action of acquiring knowledge," verbal noun from leornian (see learn). Meaning "knowledge acquired by systematic study, extensive literary and scientific culture" is from mid-14c. Learning curve attested by 1907.

Old English lar "learning, what is taught, knowledge, science, doctrine; art or act of teaching," from Proto-Germanic *laisti- (compare Old Saxon lera, Old Frisian lare, Middle Dutch lere, Dutch leer, Old High German lera, German Lehre "teaching, precept, doctrine"), from PIE root *lois- "furrow, track;" compare learn.

Proto-Indo-European root meaning "furrow, track." 

It forms all or part of: delirious; delirium; last (n.1) "wooden model of a human foot used by shoemakers;" last (v.) "endure, go on existing;" learn; learning; Lehrjahre; lore.

It is the hypothetical source of/evidence for its existence is provided by: Latin lira "furrow;" Old Prussian lyso "field bed;" Old Church Slavonic lexa "field bed, furrow;" Old High German leisa "track," Gothic laistjan "to follow," Old English læran "to teach."