If in need, it could be doubtful (10)
I believe the answer is:
indefinite
'doubtful' is the definition.
(thesaurus)
'if in need it could be' is the wordplay.
'could be' is an anagram indicator.
'if'+'in'+'need'+'it'='ifinneedit'
'ifinneedit' anagrammed gives 'INDEFINITE'.
(Other definitions for indefinite that I've seen before include "Unsettled" , "Vague" , "Like a" , "sort of article" , "Not decided or not known" .)