Glance over (4)
'glance over' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for scan that I've seen before include "convert metres into feet?" , "Study intently" , "Glance negligently at" , "Examine carefully" , "Examine intensely -- examine superficially" .)
(Other definitions for skim that I've seen before include "Move lightly over a surface" , "Brush over" , "Remove top layer; read bits of" , "Bounce (a stone) over water" , "Read quickly or remove from surface" .)