Reading a Greek letter one gives a soft audible sigh (3)
I believe the answer is:
psi
'audible sigh' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'reading a greek letter one gives a soft' is the wordplay.
I cannot really understand how this works, but
'letter' could be 's' and 's' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'soft' could be 'p' (musical abbreviation for piano, 'soft') and 'p' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for psi that I've seen before include "Greek letter; pounds per square inch (abbrev.)" , "Greek character" , "Pounds per square inch (abbr.); Greek letter" , "Greek letter; pressure unit" , "foreign letter" .)