The most common and most likely answer to this crossword clue is the 7 letter word MATINAL
I've seen this crossword clue in The Times
M
A
T
I
N
A
L
Buddy explains!
The straight part
We know that "used in morning service" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case used in morning service = matinal.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 MATINAL mean?
MATINAL adjective- In the morning, relating to the morning.