It can be slipped in a personal column (4)
I believe the answer is:
disc
This clue might be a double definition.
'it can be slipped' is the first definition.
The definition suggests a singular noun which matches the answer.
'personal column' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for disc that I've seen before include "something moving in the spine" , "Record, CD" , "Forty-five" , "Sound recording" , "Flat, circular plate - record" .)