Brief lesson absorbed by reflective handsome doctor (4)
I believe the answer is:
demo
'brief lesson' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'absorbed by reflective handsome doctor' is the wordplay.
'reflective' shows that the letters should be reversed in order.
'absorbed by' says the answer is hidden in the clue.
'omed' can be found hidden inside 'handsome doctor'.
'omed' in reverse letter order is 'DEMO'.
Can you help me to learn more?
(Other definitions for demo that I've seen before include "Brass instrument valve" , "Political protest" , "In brief, a public event as of protest under dome" , "Public protest meeting" , "Show" .)