One joins transgressive act that's a bit disgusting (5)
I believe the answer is:
sinew
'one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'transgressive act that's a bit disgusting' is the wordplay.
I cannot really understand how this works, but
'act' could be 'sin' (sin is a kind of act) and 'sin' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'joins' is the link.
Can you help me to learn more?
(Other definitions for sinew that I've seen before include "Force" , "Inelastic tissue" , "fibre" , "Muscular strength" , "Strength; tendon" .)