Sons much appreciated Mrs Harker's bottom (7)
I believe the answer is:
stamina
'bottom' is the definition.
(I've seen this before)
'sons much appreciated mrs' is the wordplay.
'sons' becomes 's'.
'much appreciated' becomes 'ta' (both are ways of saying thank you).
'mrs' becomes 'mina' ().
's'+'ta'+'mina'='STAMINA'
'harker's' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stamina that I've seen before include "capability to keep going" , "resistance" , "Energy and staying power" , "Ability for sustained effort" , "Ability to maintain effort" .)