Austere existence is seen among cats at war with mice (10)
I believe the answer is:
asceticism
'cats at war with mice' is the definition.
I can't tell whether this definition defines the answer.
'austere existence is seen among' is the wordplay.
'austere' becomes 'ascetic' (synonyms).
'existence' becomes 'm' (I can't justify this - if you can you should give a lot more credence to this answer).
'seen among' is an insertion indicator.
'ascetic'+'m'='asceticm'
'asceticm' going around 'is' is 'ASCETICISM'.
Can you help me to learn more?
(Other definitions for asceticism that I've seen before include "self-denial" , "Austerity" , "austere way of life?" , "austere lifestyle" .)