The most common and most likely answer to this crossword clue is the 9 letter word COTANGENT
C
O
T
A
N
G
E
N
T
More clues leading to the result COTANGENT
- Chap after party lapping up cheers — some function!
- Function clear, belt secured
- Function cannot get put off
- Ringing hospital department after company function
- Little thanks received by study on male function
- Can’t get on unfortunately with a concept in trigonometry
- Darken in compelling trigonometric function
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 COTANGENT mean?
COTANGENT noun- In a right triangle, the reciprocal of the tangent of an angle. Symbols: cot, ctg or ctn