Running might burn it? (3)
I believe the answer is:
fat
'running might' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'burn it?' is the wordplay.
'burn' becomes 'fa' (I can't justify this - if you can you should give a lot more credence to this answer).
'fa'+'t'='FAT'
Can you help me to learn more?
(Other definitions for fat that I've seen before include "and 24: Overpaid City type" , "Obese, having spare tyre etc" , "Like 10 ac" , "Adipose tissue" , "Substantial" .)