The most common and most likely answer to this crossword clue is the 4 plus 5 letter word LIFE EVENT
L
I
F
E
E
V
E
N
T
Buddy explains!
The straight part
We know that "marriage could be called one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marriage could be called one = life event.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.