The most common and most likely answer to this crossword clue is the 7 plus 8 letter word DOMINUS VOBISCUM
I've seen this crossword clue in The Times
D
O
M
I
N
U
S
V
O
B
I
S
C
U
M
Buddy explains!
The straight part
We know that "salutation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case salutation = dominus vobiscum.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.