Skill, by the sound of it? Definitely not (5)
I believe the answer is:
nohow
'definitely not' is the definition.
(I've seen this before)
'skill by the sound of it?' is the wordplay.
'skill' becomes 'knowhow' (I have seen 'Specialised skill' mean 'know-how' so perhaps 'skill' could also mean 'know-how').
'by the sound of it?' shows a homophone (sound like).
'knowhow' sounds like 'NOHOW'.
(Other definitions for nohow that I've seen before include "Under no circumstances (as Tweedledum said)" , "Never" , "Absolutely not in America" , "Not in any way (colloq.)" , "Not at all in US" .)