Cancel opening at 45 degrees? (6)
I believe the answer is:
negate
'cancel' is the definition.
(I've seen this before)
'opening at 45 degrees?' is the wordplay.
'opening' becomes 'gate' (a gate is an opening or entrance).
'at' means one lot of letters go next to another (I've seen this in other clues).
'45 degrees?' becomes 'ne' (I can't explain this - if you can you should believe this answer much more).
'gate' put after 'ne' is 'NEGATE'.
Can you help me to learn more?
(Other definitions for negate that I've seen before include "Disprove or nullify" , "Opera by Puccini" , "Show to be false" , "disallow!" , "Countermand" .)