The most common and most likely answer to this crossword clue is the 6 plus 8 letter word CHARON (ANCHOR)
C
H
A
R
O
N
(
A
N
C
H
O
R
)
Buddy explains!
The straight part
We know that "One supervising terminal crossing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one supervising terminal crossing = charon (anchor).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.