The most common and most likely answer to this crossword clue is the 1 letter word O
I've seen this crossword clue in The Times
O
More clues leading to the result O
- Only rotten plays were written by him
- - FRIES IS H [junk food | is | hard]
- Odd elements of party interfere
- One’s used by pirates’ swashbuckling archetype, letting out shouted ‘arr’!
- O
- 23 BANJOIST/FLAMINGO
- Order cattle by the head
- Person having to suffer American playwright
- Improve number in tavern getting drunk
- Old chap’s suppressing hint of laughter, as shown by face?
Buddy explains!

The straight part
We know that "interfere" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case interfere = o.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 O mean?
O noun- The name of the Latin-script letter O.
- A zero (used in reading out numbers).
- (IRC) Operator
- Object, see SVO
- Over
- Expression of surprise.
- Expression of wonder, amazement, or awe.
- Expression of understanding, affirmation, recognition, or realization.
- A word to precede an offhand or annoyed remark.
- A word to precede an added comment or afterthought.
- An invocation or address (similar to the vocative in languages with noun declension), often with a term of endearment.
- Exclamation for drama or emphasis (often poetic).
- Expression of pain. See ouch.
- Space filler or extra syllable, especially in (popular) music.
- (interrogative) Expression of mild scepticism.
- A word to mark a spoken phrase as imaginary.
- Expressing distance or motion.
- Expressing separation.
- Expressing origin.
- Expressing agency.
- Expressing composition, substance.
- Introducing subject matter.
- Having partitive effect.
- Expressing possession.
- Forming the "objective genitive".
- Expressing qualities or characteristics.
- Expressing a point in time.