The most common and most likely answer to this crossword clue is the 7 letter word DRILLED
I've seen this crossword clue in Financial Times
D
R
I
L
L
E
D
Buddy explains!
The straight part
We know that "Trained" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trained = drilled.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 DRILLED mean?
DRILLED verb- To create (a hole) by removing material with a drill (tool).
- To practice, especially in (or as in) a military context.
- To cause to drill (practice); to train in military arts.
- To repeat an idea frequently in order to encourage someone to remember it.
- To investigate or examine something in more detail or at a different level
- To hit or kick with a lot of power.
- To hit someone with a pitch, especially in an intentional context.
- To have sexual intercourse with; to penetrate.
- To sow (seeds) by dribbling them along a furrow or in a row.
- To cause to flow in drills or rills or by trickling; to drain by trickling.
- To entice or allure; to decoy; with on.
- To cause to slip or waste away by degrees.