Cryptic crossword clue
Classes of marine trained on board ship 8

The most common and most likely answer to this crossword clue is the 8 letter word SEMINARS

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

Buddy explains!

The straight part
We know that "Classes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case classes = seminars.
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 SEMINARS mean?

SEMINARS noun
  1. A class held for advanced studies in which students meet regularly to discuss original research, under the guidance of a professor.
  2. A meeting held for the exchange of useful information by members of a common business community.

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