The most common and most likely answer to this crossword clue is the 5 letter word SAKER
S
A
K
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R
More clues leading to the result SAKER
Buddy explains!

The straight part
We know that "falcon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case falcon = saker.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 SAKER mean?
SAKER noun- A falcon (Falco cherrug) native of Southern Europe and Asia.
- A medium cannon slightly smaller than a culverin developed during the early 17th century.