Son is able to read (4)
I believe the answer is:
'read' is the definition.
(I know that read can be written as scan)
'son is able to' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'is able to' becomes 'can' (if you can do something you are able to do it).
(Other definitions for scan that I've seen before include "Medical examination" , "Type of examination" , "Survey, maybe by X-ray" , "Skim; examine" , "Examine intensely -- examine superficially" .)