Endless lure shown by strange modesty (7)
I believe the answer is:
decorum
'modesty' is the definition.
(I've seen this before)
'endless lure shown by strange' is the wordplay.
'endless' means to remove the last letter.
'lure' becomes 'decoy' (decoying is a kind of luring).
'shown by' is a charade indicator (letters next to each other).
'strange' becomes 'rum' (I've seen this before).
'decoy' with its last letter taken away is 'deco'.
'deco'+'rum'='DECORUM'
(Other definitions for decorum that I've seen before include "modesty" , "Dignity of behaviour or procedure" , "Propriety in manners and conduct" , "good behaviour" , "(Of outward appearances) what is proper" .)