tra•bec•u•la. 1. a structural body part that resembles a beam or a crossbar. 2. any of the barlike tissue structures that extend across the cavity in a plant duct or sac, as in the sporangium of a moss. trabēcula, Latin: little beam]. tra•bec′u•lar, tra•bec′u•late (-lɪt, -ˌleɪt) adj.