The most common and most likely answer to this crossword clue is the 5 letter word BASAL
I've seen this crossword clue in Independent
B
A
S
A
L
More clues leading to the result BASAL
Buddy explains!

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 BASAL mean?
BASAL noun- Base, bottom, minimum
- Any basal structure or part
- Basic, elementary; relating to, or forming, the base, or point of origin.
- Associated with the base of an organism or structure.
- Of a minimal level that is necessary for maintaining the health or life of an organism.
- In a phylogenetic tree, being a group, or member of a group, which diverged earlier. The earliest clade to branch in a larger clade.