"I arrive at the dining room."
Translation:Ad cenaculum advenio.
They're not synonyms, although the lack of context should permit both answers.
A triclinium is not a room per se, just an arrangement of three (tri) couches (clinia) where rich Romans ate while reclining, just like their decadent Greek forbears.
A cenaculum is literally the room (culum) where you eat dinner (cena).