Lies endlessly and spuriously claims it's not true (6)
I believe the answer is:
denial
'not true' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'lies endlessly and spuriously claims it's' is the wordplay.
I cannot quite see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
The remaining letters 'dial' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for denial that I've seen before include "Repudiation" , "Negation" , "Refusal to accept an unpalatable truth" , "Daniel (anag.)" , "Rejection or refusal" .)