The most common and most likely answer to this crossword clue is the 9 letter word FRATERNAL
I've seen this crossword clue in Financial Times
F
R
A
T
E
R
N
A
L
More clues leading to the result FRATERNAL
- Father and a bird most of all related
- Female singer backing way to restrict right of society men?
- Like some twins for a threesome initially? Run during way over
- Value our sailors in river like brothers
- Excited, ran after head of lodge – masonic, perhaps
- Monk-like, ran after screwing on top of lecturer
- Monastic fellow learnt a different way to be brotherly
Buddy explains!

The straight part
We know that "brotherly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case brotherly = fraternal.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 FRATERNAL mean?
FRATERNAL noun- A society formed to provide mutual aid, such as insurance.
- A fraternal twin.
- Of or pertaining to a brother or brothers.
- Of or pertaining to a fraternity.
- Platonic or friendly.
- Of twins or embryos, produced from two different eggs and sperm, and genetically distinct.