The most common and most likely answer to this crossword clue is the 7 letter word TESTING
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Buddy explains!

The straight part
We know that "Difficult/trial" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case difficult/trial = testing.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 TESTING mean?
TESTING verb- To challenge.
- To refine (gold, silver, etc.) in a test or cupel; to subject to cupellation.
- To put to the proof; to prove the truth, genuineness, or quality of by experiment, or by some principle or standard; to try.
- (academics) To administer or assign an examination, often given during the academic term, to (somebody).
- To place a product or piece of equipment under everyday and/or extreme conditions and examine it for its durability, etc.
- To be shown to be by test.
- To examine or try, as by the use of some reagent.
- To attest (a document) legally, and date it.
- To make a testament, or will.
- The act of conducting a test; trialing, proving.
- Difficult, tough