Collins Chinese Dictionary Plus (3rd edition), 2011:
哎
āi 叹
1 (表示惊讶或不满) oh
- 哎!这(這)么(麼)贵(貴)! Āi! Zhème guì! Oh! It's so expensive!
2 (表示提醒) hey
- 哎!别(別)踩了那朵花。 Āi! Bié cǎile nà duǒ huā. Hey! Careful not to tread on that flower.