Unwilling to shelter adult a little is detestable (9)
I believe the answer is:
loathsome
'is detestable' is the definition.
(I've seen this in another clue)
'unwilling to shelter adult a little' is the wordplay.
'unwilling' becomes 'loth' (similar in meaning).
'to shelter' indicates putting letters inside.
'adult' becomes 'a' (abbreviation).
'a little' becomes 'some' (both can mean a small amount).
'loth' placed around 'a' is 'loath'.
'loath'+'some'='LOATHSOME'
(Other definitions for loathsome that I've seen before include "Disgusting, nauseating" , "Detestable" , "15 [ABHORRENT]" , "Hateful" , "gross" .)