It’s painful on tablet: patient that’s on bed (10)

I believe the answer is:

pillowcase

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'bed' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'it's painful on tablet patient that's on' is the wordplay.
'it's painful on tablet' becomes 'pillow' (I can't explain this - if you can you should believe this answer much more).
'patient' becomes 'case' (synonyms).
'that's on' means one lot of letters go next to another.
'pillow'+'case'='PILLOWCASE'

Can you help me to learn more?

(Other definitions for pillowcase that I've seen before include "Item of bed linen" , "Item of bedlinen" .)

I've seen this clue in The Guardian.

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