Frivolous, dissipated, welcoming British drizzle (14)
I believe the answer is:
scatterbrained
'frivolous' is the definition.
(thesaurus)
'dissipated welcoming british drizzle' is the wordplay.
'dissipated' becomes 'scattered' ('scatter' can be a synonym of 'dissipate').
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'british drizzle' becomes 'brain' (I can't explain this - if you can you should believe this answer much more).
'scattered' enclosing 'brain' is 'SCATTERBRAINED'.
Can you help me to learn more?
(Other definitions for scatterbrained that I've seen before include "Inattentive" , "Disorganised, lacking concentration" , "Unfocused" , "Inclined to forget" , "Disorganised and unable to concentrate" .)