Dad loses out, a complete failure (4,4)
I believe the answer is:
dead loss
'a complete failure' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'dad loses out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'dad'+'loses'='dadloses'
'dadloses' with letters rearranged gives 'DEAD LOSS'.
Can you help me to learn more?
(Other definitions for dead loss that I've seen before include "write-off" , "unprofitable" , "Dud" , "Totally useless item" , "Useless person or thing - sounds moribund and profitless" .)