The Portuguese word for uncle is
tio

Gender

The gender of tio is masculine. E.g. o tio.

The plural of tio is tios.

uncle
1. Substantivo. tio

tio
1. n-m. uncle (brother of someone's father or mother, or an aunt's husband)
2. n-m. (Brazil, colloquial, often, considered disrespectful) uncle (term of address for any adult)
3. n-m. (usually in the diminutive) guy; bloke
Tinha dois tiozinhos no ponto. - There were two guys at the bus stop.
4. n-m. an employee who performs a given activity
tio da limpeza - uncle of the cleaning