Less than attractive enterprise (11)
I believe the answer is:
undertaking
'enterprise' is the definition.
(thesaurus)
'less than attractive' is the wordplay.
'less than' becomes 'under' (I've seen this before).
'attractive' becomes 'taking' ('taking' can be similar in meaning to 'attractive').
'under'+'taking'='UNDERTAKING'
(Other definitions for undertaking that I've seen before include "Formal promise; company" , "Task" , "Solemn business" , "pledge" , "Promise, business" .)