Cryptic crossword clue
Servant a long time retained by vessel’s bosses 4,8

The most common and most likely answer to this crossword clue is the 4 plus 8 letter word LINE MANAGERS

I've seen this crossword clue in The Sunday Telegraph
L
I
N
E
M
A
N
A
G
E
R
S

Buddy explains!

The straight part
We know that "bosses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bosses = line managers.
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.

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