The most common and most likely answer to this crossword clue is the 5 letter word CHOCK
C
H
O
C
K
More clues leading to the result CHOCK
Buddy explains!

The straight part
We know that "Secure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case secure = chock.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 CHOCK mean?
CHOCK noun- Any object used as a wedge or filler, especially when placed behind a wheel to prevent it from rolling.
- Any fitting or fixture used to restrict movement, especially movement of a line; traditionally was a fixture near a bulwark with two horns pointing towards each other, with a gap between where the line can be inserted.
- To stop or fasten, as with a wedge, or block; to scotch.
- To fill up, as a cavity.
- To insert a line in a chock.
- Entirely; quite.
- An encounter.
- To encounter.
- To make a dull sound.