Happy entertaining loose collection of stars (6)
I believe the answer is:
galaxy
'collection of stars' is the definition.
(I've seen this before)
'happy entertaining loose' is the wordplay.
'happy' becomes 'gay' ('gay' can be similar in meaning to 'happy').
'entertaining' indicates putting letters inside.
'loose' becomes 'lax' ('lax' is associated in meaning with 'loose').
'gay' going around 'lax' is 'GALAXY'.
(Other definitions for galaxy that I've seen before include "Lots of stars" , "Spiral, elliptical, group of stars" , "Division of the universe" , "e.g. The Milky Way" , "The Milky Way, for example" .)