The Chinese word for aunt is
阿姨

ā yí

Chinese Definition

aunt
1. 名词. 姑母，姨母，伯母，婶母，舅母
2. 名词. （儿语）阿姨
Components
阿
1. (Prefix used in front of the surname or last character of someone’s given name to express familiarity or friendliness (traditionally used in rural or southern Chinese dialects).)
(Alternative form 亞)
阿爸 - dad
阿 @扁 - Ah Bian (Chen Shui-bian)
《阿Qqiū 正傳zhuàn》 - The True Story of Ah Q
2. (Hokkien, honorific) (Prefix to rank seniority for kinship terms.)
阿兄 - eldest brother, MN
3. (Northern Wu, including Suzhou) (Interrogative particle)
倷阿姓趙？ - Is your surname Zhao?, W-SZ, ref=1993, 蘇州方言詞典, page 20
4. Alternative form of 啊 (ā, á, ǎ, à, a, t=particle)
5. Short for 阿富汗 (Afghanistan)
6. Short for 阿爾巴尼亞 (Albania)
7. Short for 阿拉伯 (Arabic)
8. atto- (SI unit prefix)
9. big mound; mountain
10. hillside
11. fine silks
12. (literary, of a mountain or stream) bend; corner
13. waterside
14. nearby; near
15. to flatter; to pander to
阿ē諛奉承 - sweet-talking
16. to be unfairly partial to
17. Alternative form of 屙 (to excrete)
姨
1. maternal aunt (mother's sister)
二姨 - mother's second eldest sister
2. sister-in-law (wife's sister)
3. aunt (a term of address for a woman around one's mother's age or slightly younger)
4. (historical) father's concubine

阿姨
1. n. (informal, affectionate) maternal aunt (mother's sister or female cousin)
她萬萬沒想到她的阿姨是殺手。 - She never suspected for a minute that her aunty was a killer.
2. n. (Cantonese) one's mother's younger sister
3. n. (affectionate) auntie (form of address for any woman around one's mother's age)
4. n. (a form of address for working-age female caretakers, including nurses, cleaning ladies, live-in staff, etc.)
5. n. (euphemistic) mom; mother