Meaning

verb make plain and comprehensible

verb define

verb serve as a reason or cause or justification of

originFrom Middle English explanen, from Old French explaner, from Latin explanō (“to flatten, spread out, make plain or clear, explain”), from ex- (“out”) + planō (“to flatten, make level”), from planus (“level, plain”); see plain and plane. Compare esplanade, splanade. Displaced Old English reċċan.

Etymology from Wiktionary, CC BY-SA 3.0