Prepare for scan on the Fourth of July (5)
I believe the answer is:
ready
'prepare' is the definition.
('ready' can be a synonym of 'prepare')
'scan on the fourth of july' is the wordplay.
'scan' becomes 'read' ('read' can be a synonym of 'scan').
'on' means one lot of letters go next to another.
'the fourth of july' becomes 'y' (fourth letter of the word 'July').
'read'+'y'='READY'
'for' is the link.
(Other definitions for ready that I've seen before include "Fully-prepared" , "Poised for action" , "Prepare < dough" , "Quick" , "Intelligent" .)