The most common and most likely answer to this crossword clue is the 6 letter word MISSAL
M
I
S
S
A
L
More clues leading to the result MISSAL
- Fail to understand a line in prayer book
- Service book - a weapon for Americans, do we hear?
- Girl, a learner, getting book in church
- Girl and boy married with prayer book
- Islam’s enigmatic religious book
- Religious book for a young lady — a student
- Islam’s regulated prayer book
- Skip a line in prayer book
- Book young woman, a learner driver
- Omit a learner's letter
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 = missal.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 MISSAL mean?
MISSAL noun- A prayer book
- A book containing the prayers and responses needed when celebrating the Roman Catholic Mass throughout the year