The most common and most likely answer to this crossword clue is the 6 letter word ATTORN
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The straight part
We know that "Accept new tenancy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case accept new tenancy = attorn.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ATTORN mean?
ATTORN verb- To transfer one's obligations from a person to another person.
- To consent to the transfer of one's obligations as tenant under a lease to a new landlord.
- To acknowledge the jurisdiction of (a particular court) over one's dispute.