From Latin 'lectura' (a reading) — medieval teaching was literally reading aloud from texts, same root as 'legend.'
An educational talk given to an audience, especially to students at a university, or a long serious speech of warning or reproof.
From Medieval Latin 'lectūra' (a reading), from Latin 'lectus,' past participle of 'legere' (to read, to gather, to choose), from PIE *leǵ- (to gather, to collect). A 'lecture' was originally simply a reading aloud — in the medieval university, a professor literally read from an authoritative text while students took notes. The shift from 'reading' to 'speaking' reflects the evolution of university teaching from recitation of existing texts to original discourse
In the medieval university, a 'lecture' was literally a reading — the professor read from an approved text (often the only copy in the room) while students copied it down word for word. The word still means 'reading' in French ('lecture') and in German 'Lektüre' means reading material. Only in English has it shifted entirely to mean an oral presentation.