The most common and most likely answer to this crossword clue is the 8 letter word FISTULAE
F
I
S
T
U
L
A
E
Buddy explains!

The straight part
We know that "calami" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calami = fistulae.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 FISTULAE mean?
FISTULAE noun- An abnormal connection or passageway between organs or vessels that normally do not connect.
- A tube, a pipe, or a hole.
- The tube through which the wine of the Eucharist was once sucked from the chalice.