Bill to rent out computer (6)
I believe the answer is:
tablet
'computer' is the definition.
'bill to rent' is the wordplay.
'bill' becomes 'tab' (a tab is a bill at a bar).
'to rent' becomes 'let' ('let' can be a synonym of 'rent').
'tab'+'let'='TABLET'
'out' is the link.
(Other definitions for tablet that I've seen before include "Medicine - flat slab - computer" , "pill needed" , "Pill; computer" , "Small slab or flat pill" , "panel with an inscription" .)