Paint – gallons oddly used on front of store (5)
I believe the answer is:
gloss
'paint' is the definition.
(I have seen 'Shiny paint ' mean 'gloss' so perhaps 'paint' could also mean 'gloss')
'gallons oddly used on front of store' is the wordplay.
'oddly' indicates alternate letters.
'used on' says to put letters next to each other.
'front of' says to take the initial letters.
The first letter of 'store' is 's'.
The alternating letters of 'gallons' are 'glos'.
'glos'+'s'='GLOSS'
(Other definitions for gloss that I've seen before include "Misleading explanation" , "translation" , "Superficial shine" , "Shiny type of paint" , "Very shiny finish" .)