Happy to host loose group of stars (6)
I believe the answer is:
galaxy
'group of stars' is the definition.
(I've seen this before)
'happy to host loose' is the wordplay.
'happy' becomes 'gay' (similar in meaning).
'to host' indicates putting letters inside (inserted letters are hosted or welcomed).
'loose' becomes 'lax' (synonyms).
'gay' placed around 'lax' is 'GALAXY'.
(Other definitions for galaxy that I've seen before include "Vast number of stars" , "A large independent system of stars" , "host" , "Large star system" , "Collection of star systems (made of chocolate?)" .)