The most common and most likely answer to this crossword clue is the 6 letter word AWEIGH
I've seen this crossword clue in The Guardian
A
W
E
I
G
H
Buddy explains!

The straight part
We know that "Just off the bottom" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case just off the bottom = aweigh.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 AWEIGH mean?
AWEIGH adjective- Just drawn out of the ground, and hanging perpendicularly; atrip; said of the anchor.