Meaning of Y in English

I. Y BrE AmE , y /waɪ/ ( plural Y’s , y’s ) noun

[uncountable and countable] the 25th letter of the English alphabet

⇨ ↑ Y chromosome , ↑ Y-fronts

II. Y, the /waɪ/ BrE AmE American English informal

the YMCA or YWCA:

She was staying in a room at the Y.

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.