A relative by marriage is in the legal profession (2-3)
I believe the answer is:
in-law
'a relative by marriage' is the definition.
(I've seen this before)
'in the legal profession' is the wordplay.
I cannot quite see how this works, but
'in' is within the answer.
'profession' could be 'law' (law is a kind of profession) and 'law' is located in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for in-law that I've seen before include "Meghan to Harry's family?" , "Near relative" , "Family member, by marriage" , "Relative by marriage" , "Relation by marriage" .)