I’ll try to do feller harm, describing relative as posh minor (6,4,10)

'i'll try to do feller harm' is the definition.
I can't tell whether this defines the answer.

'relative as posh minor' is the wordplay.
I cannot really see how this works, but
'relative' could be 'aunt' (aunt is a kind of relative) and 'aunt' is present in the answer.
'minor' could be 'little' (similar in meaning) and 'little' is present in the answer.
This explanation may well be incorrect...

'describing' is the link.

Can you help me to learn more?