An Etymological Dictionary of Astronomy and Astrophysics

1. A title or explanation for a picture or illustration, especially in a magazine.
   

2. A heading or title, as of a chapter, article, or page (Dictionary.com).

Etymology (EN): M.E. capcio(u)n “taking, seizure,” from capcion “arrest, capture, imprisonment,” or directly from L. caption-, from capt(us) “taken,” → capture.

Etymology (PE): Kapéš “taking, capture,” verbal noun from kapidan
“to seize, take, capture,” related to qâpidan, qâp zadan “to rob, to seize,” Malâyeri qapâl “robbing, seizure, robbing,” probably related to L. capere, → capture.