Type of star (3,5)
'type of star' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for red giant that I've seen before include "big star" , "Large low-temperature star" , "Large, cool bright star" , "Megastar" , "Cool, immense star of high luminosity" .)
(Other definitions for red dwarf that I've seen before include "Small, cool star - TV show" , "Old cool star" , "Small old cooling star" .)