Why is the ninth month called September?
early 15c., "maturity of character;" mid-15c., "ripeness," from Middle French maturité and directly from Latin maturitatem (nominative maturitas) "ripeness," from maturus "ripe" (see mature (v.)). Financial sense "state of being due for payment" is from 1815.
maturity ma·tu·ri·ty (mə-tyur'ĭ-tē, -tur'-, -chur'-)
The state or quality of being fully grown or developed.
The state or quality of being mature.