woman past her prime; older matron
A somewhat dated or blunt term for a woman who is no longer young, often implying she is well past marriageable age or visibly aging. Can carry a derogatory or pitying tone; use with caution.
She's already past her prime, so marriage will probably be difficult.
That older actress is still active on stage.
おばさん is a general term for a middle-aged woman, often used neutrally or familiarly, whereas 大年増 is more pointed and old-fashioned.
Compound of 大 (おお, 'great') + 年増 (どしま, 'woman past her youth'). The reading どしま is a sound shift from としま (年増).