The most common and most likely answer to this crossword clue is the 3 letter word COL
I've seen this crossword clue in The Times
C
O
L
More clues leading to the result COL
Buddy explains!

The straight part
We know that "Senior officer/pass" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case senior officer/pass = col.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 COL mean?
COL noun- A dip on a mountain ridge between two peaks.
- A pressure region between two anticyclones and two low-pressure regions.