The most common and most likely answer to this crossword clue is the 6 letter word NEGATE
N
E
G
A
T
E
More clues leading to the result NEGATE
- Discredit wife leaving prison
- Declare invalid's wife released from old London gaol
- Deny access to Tyneside region?
- Deny women’s being released from old prison
- Deny in former London prison losing weight
- Deny most of teenage mucking about
- Deny worried by information on reflection
- Wipe out revolutionary in The Secret Agent
- Invalidate points given to paying supporters
- Deny point took in about Goliath
Buddy explains!

The straight part
We know that "Nullify" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nullify = negate.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 NEGATE mean?
NEGATE verb- To deny the existence, evidence, or truth of; to contradict.
- To nullify or cause to be ineffective.
- To be negative; bring or cause negative results.
- To perform the NOT operation on.