What is Vishnu's gender?

The traditional Sanskrit explanation of the name Vishu involves the root viś, meaning "to settle, to enter", or also (in the Rigveda) "to pervade", and a suffix nu, translating to approximately "the All-Pervading One". An early commentator on the Vedas, Yaska, in his Nirukta, defines Vishnu as 'vishnu vishateh; one who enters everywhere', and 'yad vishito bhavati tad vishnurbhavati; that which is free from fetters and bondages is Vishnu.'

However, as the name is of one of the male trinity of Hindu gods, it is a male name.

Vaishnavi (sanskrit, feminine form of Vaishnava) is a legendary figure in the Hindu tradition and the consort of Lord Vishnu.