Lift bottom line up for an LBD, perhaps (8,5)
I believe the answer is:
cocktail dress
'an lbd perhaps' is the definition.
(LBD is an abbreviation for little black dress)
'lift bottom line up' is the wordplay.
'lift' becomes 'cock' (for example, cocking a rifle).
'bottom' becomes 'tail' ('tail' can be a synonym of 'bottom'**).
'line up' becomes 'dress' ('dress' can be a synonym of 'line up').
'cock'+'tail'+'dress'='COCKTAIL DRESS'
'for' is the link.
(Other definitions for cocktail dress that I've seen before include "semi-formal wear" , "Black tie for ladies?" .)