Mistakenly seek, with hideous man, joint tenderness? (10,4)
I believe the answer is:
housemaids knee
'joint tenderness?' is the definition.
(I've seen this before)
'mistakenly seek with hideous man' is the wordplay.
'mistakenly' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'hideous'+'man'='hideousman'
'seek' put after 'hideousman' is 'hideousmanseek'.
'hideousmanseek' with letters rearranged gives 'HOUSEMAIDS KNEE'.
(Other definitions for housemaids knee that I've seen before include "complaint to a servant?" , "Joint inflammation" , "joint tenderness" .)