The most common and most likely answer to this crossword clue is the 10 letter word ASSOCIATES
I've seen this crossword clue in The Guardian
A
S
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Buddy explains!
The straight part
We know that "Allies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case allies = associates.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 ASSOCIATES mean?
ASSOCIATES noun- A person united with another or others in an act, enterprise, or business; a partner.
- Somebody with whom one works, coworker, colleague.
- A companion; a comrade.
- One that habitually accompanies or is associated with another; an attendant circumstance.
- A member of an institution or society who is granted only partial status or privileges.
- One of a pair of elements of an integral domain (or a ring) such that the two elements are divisible by each other (or, equivalently, such that each one can be expressed as the product of the other with a unit).
- To join in or form a league, union, or association.
- To spend time socially; keep company.
- (with with) To join as a partner, ally, or friend.
- To connect or join together; combine.
- To connect evidentially, or in the mind or imagination.
- (in deliberative bodies) To endorse.
- To be associative.
- To accompany; to be in the company of.