The most common and most likely answer to this crossword clue is the 8 letter word OVERRIDE
I've seen this crossword clue in The Guardian
O
V
E
R
R
I
D
E
More clues leading to the result OVERRIDE
- Rule against sin seen in video nasty
- Foreign order I’ve set aside
- Reverse up drive
- Cancel order I’ve put out
- Countermand order I’ve set in motion
- Take manual control of extra attraction at fairground
- Supersede order I’ve sent out
- Take manual control of complete drive
- Ignore end of verse after poet admits blunder
- Control where plane above IOW may be heard
Buddy explains!

The straight part
We know that "Cancel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cancel = override.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 OVERRIDE mean?
OVERRIDE noun- A mechanism, device or procedure used to counteract an automatic control.
- A royalty.
- A device for prioritizing audio signals, such that certain signals receive priority over others.
- A method with the same name and signature as a method in a superclass, which runs instead of that method, when an object of the subclass is involved.
- To ride across or beyond something.
- To ride a horse too hard.
- To counteract the normal operation of something; to countermand with orders of higher priority.
- To define a new behaviour of a method by creating the same method of the superclass with the same name and signature.