Face time having lost case and significance (12)
I believe the answer is:
impertinence
'face' is the definition.
(thesaurus)
'time having lost case and significance' is the wordplay.
I cannot really see how this works, but
'time' could be 't' (abbreviation) and 't' is found within the answer.
'case' could be 'imp' and 'imp' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for impertinence that I've seen before include "Insolence" , "Disrespectful behaviour" , "Lack of respect" , "cheek or lip" , "Rudeness" .)