Diminutive underground guard (5)
I believe the answer is:
gnome
This could be a double definition.
'diminutive' is the first definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'underground guard' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I don't see?
Can you help me to learn more?
(Other definitions for gnome that I've seen before include "Dwarf (found in garden?)" , "Little garden person?" , "Fairy-tale creature, in the garden perhaps" , "Fairytale dwarf, often in garden" , "Mythical creature" .)