Ray and Mark well captivated by a muse dancing (7)
I believe the answer is:
sunbeam
'ray' is the definition.
(I know that sunbeam is a type of ray)
'mark well captivated by a muse dancing' is the wordplay.
'mark well' becomes 'nb' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'captivated by' indicates putting letters inside.
'dancing' indicates anagramming the letters.
'a'+'muse'='amuse'
'amuse' anagrammed gives 'sueam'.
'nb' going within 'sueam' is 'SUNBEAM'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for sunbeam that I've seen before include "Bright shaft of daylight" , "Bright ray -- bus name (anag)" , "sheds a bit of light" , "Ray of natural light" , "Ray of solar light" .)