astrophysics

UK: /ˌæstrəʊˈfɪzɪks/ US: /ˌæstroʊˈfɪzɪks/ ,(as′trō fiz′iks)

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

as•tro•phys•ics /ˌæstroʊˈfɪzɪks/   n. [uncountable; used with a singular verb]

1. Astronomy the branch of astronomy that deals with the physical properties of celestial bodies and the interaction between matter and radiation.

as•tro•phys•i•cist /ˌæstroʊˈfɪzəsɪst/  n. [countable]

WordReference Random House Unabridged Dictionary of American English © 2026

as•tro•phys•ics  (as′trō fiz′iks), n. (used with a sing. v.)

1. Astronomy the branch of astronomy that deals with the physical properties of celestial bodies and with the interaction between matter and radiation in the interior of celestial bodies and in interstellar space.

• 1885–90; astro- + physics

as′tro•phys′i•cal, adj. 
as•tro•phys•i•cist  (as′trō fiz′ə sist), n. 

Collins Concise English Dictionary © HarperCollins Publishers::

astrophysics / ˌæstrəʊˈfɪzɪks/ noun

1. (functioning as singular) the branch of physics concerned with the physical and chemical properties, origin, and evolution of celestial bodies

ˌastroˈphysicist noun