atrial

WordReference Random House Learner's Dictionary of American English © 2026

a•tri•um /ˈeɪtriəm/   n. [countable] , pl. a•tri•a /ˈeɪtriə/  a•tri•ums. 

1. Architecture
   • a central courtyard open to the sky, or a lobby with a skylight.
   • the main or central room of an ancient Roman house, open to the sky at the center.
2. Anatomy a hollow space in the body, esp. one of the two upper chambers of the heart.

a•tri•al, adj. 

WordReference Random House Unabridged Dictionary of American English © 2026

a•tri•um  (ā′trē əm), n., pl. a•tri•a (ā′trē ə), a•tri•ums. 

1. Architecture
   • Also called cavaedium. the main or central room of an ancient Roman house, open to the sky at the center and usually having a pool for the collection of rain water.
   • a courtyard, flanked or surrounded by porticoes, in front of an early or medieval Christian church. See diag. under basilica. 
   • a skylit central court in a contemporary building or house.
2. Anatomy either of the two upper chambers on each side of the heart that receive blood from the veins and in turn force it into the ventricles. See illus. under heart. 

• Neo-Latin)
• Latin (in anatomical sense
• 1570–80

a′tri•al, adj.