The fewest possibly decimated (3)
I believe the answer is:
ten
'decimated' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives sometimes define each other.
'the fewest' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'fewest' becomes 'en' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
't'+'en'='TEN'
'possibly' is the link.
Can you help me to learn more?
(Other definitions for ten that I've seen before include "honour" , "Half a score" , "No of sides of a decagon" , "time" , "Very young" .)