Cover opening of store in advance of publicity? (6)
I believe the answer is:
spread
'cover' is the definition.
(spreading is a kind of covering)
'opening of store in advance of publicity?' is the wordplay.
'opening of' indicates taking the first letters.
'in advance of' becomes 'pre' ('pre' means before).
'publicity?' becomes 'ad' (short for advert).
The initial letter of 'store' is 's'.
's'+'pre'+'ad'='SPREAD'
(Other definitions for spread that I've seen before include "Broadcast" , "Scatter or distribute more thinly" , "Extent; elaborate meal" , "Diffuse" , "we hope to avoid in middle age" .)