one's late mother; deceased mother
Used to refer to one's own mother who has passed away. Often appears in formal or written contexts, such as obituaries, memoirs, or respectful speech.
I am sorting through my late mother's belongings.
I wrote a song dedicated to my late mother.
亡き is the fossilized attributive form of the classical adjective 亡し, “dead; deceased,” modifying 母, “mother.”