Tongue obtained from farm animal having rested over time (3,5)
I believe the answer is:
pig latin
'tongue' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?
'farm animal having rested over time' is the wordplay.
'farm animal' becomes 'pig' (I've seen this before).
'having' means one lot of letters go next to another.
'rested over time' becomes 'latin' (I am not sure about this - if you are sure you should believe this answer much more).
'pig'+'latin'='PIG LATIN'
'obtained from' acts as a link.
Can you help me to learn more?
(Another definition for pig latin that I've seen is " secret language".)