Falsehood needed to put right a big town? (9)
I believe the answer is:
mendacity
'falsehood' is the definition.
(thesaurus)
'to put right a big town?' is the wordplay.
'to put right' becomes 'mend' (I've seen this in another clue).
'big town?' becomes 'city' (I've seen this before).
'mend'+'a'+'city'='MENDACITY'
'needed' is the link.
(Other definitions for mendacity that I've seen before include "Untruthfulness" , "Lying" , "Quality or habit of telling lies or being deceitful" .)