Cretan lied appallingly in testimony (10)
I believe the answer is:
credential
'testimony' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'cretan lied appallingly' is the wordplay.
'appallingly' indicates anagramming the letters (I've seen this in other clues).
'cretan'+'lied'='cretanlied'
'cretanlied' anagrammed gives 'CREDENTIAL'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for credential that I've seen before include "Official introductory letter" , "Interlaced (anag.)" , "Qualification (indicating a person's suitability)" , "proof of entitlement" .)