Words used to threaten family members in Old English (2,4)
I believe the answer is:
or else
'words used to threaten family' is the definition.
I can't judge whether this definition defines the answer.
'members in old english' is the wordplay.
'members' becomes 'rels' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'old english' becomes 'oe'.
'rels' inserted into 'oe' is 'OR ELSE'.
Can you help me to learn more?
(Other definitions for or else that I've seen before include "Threatening phrase" , "Otherwise - may be threatening" , "Otherwise - that's a threat" , "Vague threat" , "Alternatively" .)