Attractiveness of girl on vacation having affair (7)
I believe the answer is:
glamour
'attractiveness' is the definition.
(I've seen this before)
'girl on vacation having affair' is the wordplay.
'on vacation' means to remove the middle letters.
'having' says to put letters next to each other.
'affair' becomes 'amour' (synonyms).
'girl' with its centre taken out is 'gl'.
'gl'+'amour'='GLAMOUR'
'of' acts as a link.
(Other definitions for glamour that I've seen before include "appeal" , "Alluring beauty, romantic aura" , "Fascinating beauty" , "Charm and allure" , "Alluring quality" .)