姨妈 (姨媽) yímā

yímā noun mother's sister; maternal aunt
Domain: Modern Chinese 现代汉语 , Subdomain: Family , Concept: Relative 亲戚
Notes: 舅父 is a formal term, in contast to 阿姨, which means the same thing but is informal (CC-CEDICT '姨媽'; Guoyu '姨媽'; Sun 2006, loc. 977)

Also contained in

大姨妈 、 姨妈巾