accrētĭo, ōnis, f. [accresco],
an increasing , increment : lunam accretione et deminutione luminis ... significantem dies, Cic. Tusc. 1, 28, 68.
accrētiō ōnis, f accresco, an increase (once): luminis, i. e. the waxing of the moon. ...
An Elementary Latin Dictionary