The adjective taciturn describes someone who is very quiet, does not say much or is reserved. This person could seem unfriendly for being uncommunicative. 

Synonyms are close-moutheddistant, reserved, or reticent.

The word origins from Middle French (15th century) taciturne and from Latin taciturnus and tacitus meaning “not talkative, noiseless”.

I don’t know him that much but he’s obviously a taciturn.

Jake and Ryle are both taciturn, I admire their friendship for being so strong without having much conversation.

We were friends since grade school but didn’t know she’s a taciturn at home until we became roommates.