The most common and most likely answer to this crossword clue is the 6 letter word ALIGNS
I've seen this crossword clue in Financial Times
A
L
I
G
N
S
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 = aligns.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 ALIGNS mean?
ALIGNS verb- To form a line; to fall into line.
- To adjust or form to a line; to range or form in line; to bring into line.
- To store (data) in a way that is consistent with the memory architecture, i.e. by beginning each item at an offset equal to some multiple of the word size.
- To identify with or match the behaviour, thoughts, etc of another person.
- To organize a linear arrangement of DNA, RNA or protein sequences which have regions of similarity.