Mathematical expressions only half written down in class (4)
I believe the answer is:
form
'class' is the definition.
(I know that class can be written as form)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for form that I've seen before include "Establish" , "Home of a hare" , "Acceptable conduct" , "Shape - document to be filled in" , "Class in a school, or the shape of something" .)