The most common and most likely answer to this crossword clue is the 5 letter word EXERT
I've seen this crossword clue in Independent
E
X
E
R
T
More clues leading to the result EXERT
- Use ash, perhaps, when covering cross up
- Apply authority without power
- Bring into play, as river king, leading Thespian
- Employ specialist to remove piano
- Exercise that Rex expects back in this
- Virtuoso lacking power to bring into use
- English king back on throne’s beginning to make an effort
- Make a strenuous effort to disregard hint of presumption in scientific witness
- Specialist after releasing pressure put in effort
- Apply to be specialist? No pressure!
Buddy explains!

The straight part
We know that "Make a strenuous effort" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case make a strenuous effort = exert.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 EXERT mean?
EXERT verb- To put in vigorous action.
- To make use of, to apply, especially of something non-material.