Cats perhaps calm us in distress, one’s gathered (7)
I believe the answer is:
musical
'cats perhaps' is the definition.
(Cats is an Andrew Lloyd Webber musical)
'calm us in distress one's gathered' is the wordplay.
'in distress' indicates anagramming the letters.
'one' becomes 'I' (Roman numeral).
'gathered' means one lot of letters goes inside another.
'calm'+'us'='calmus'
'calmus' anagrammed gives 'muscal'.
'muscal' enclosing 'i' is 'MUSICAL'.
(Other definitions for musical that I've seen before include "Eg, Les Miserables" , "Euphonious" , "Melodic" , "Rent for one" , "Tuneful; stage work" .)