Dad's second jumper, for instance, shows full value (6)
I believe the answer is:
amount
'value' is the definition.
(I've seen this before)
'dad's second jumper for instance shows full' is the wordplay.
I cannot quite understand how this works, but
'second' could be 'mo' (both are short periods of time) and 'mo' is present in the answer.
The remaining letters 'aunt' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for amount that I've seen before include "Total or extent" , "A quantity or total of anything" , "Measure, quantity" , "Add up or be equivalent to" , "Supply" .)