Tall story accepted by an outsider (5)
I believe the answer is:
alien
'outsider' is the definition.
(thesaurus)
'tall story accepted by an' is the wordplay.
'tall story' becomes 'lie'.
'accepted by' indicates putting letters inside.
'lie' placed inside 'an' is 'ALIEN'.
(Other definitions for alien that I've seen before include "of foreigners" , "Clanger?" , "Being from another world" , "Foreign, strange" , "One is from outer space, perhaps" .)