The most common and most likely answer to this crossword clue is the 5 letter word AITCH
I've seen this crossword clue in The Times
A
I
T
C
H
More clues leading to the result AITCH
- Letter revealing a union problem after seven years?
- Character initially dug out of a hole
- Letter that's not delivered in Hackney?
- A desire that I will immediately succeed
- Admirer's initial longing to construct a letter
- A tickly sensation that starts hurting
- American leader comes to Long Beach at last!
- Letter, a ticklish thing
- A long letter
- A desire that’s often unexpressed in Bow
Buddy explains!

The straight part
We know that "Letter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case letter = aitch.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 AITCH mean?
AITCH noun- The name of the Latin-script letter H.