The most common and most likely answer to this crossword clue is the 10 letter word NETHERMOST
I've seen this crossword clue in The Daily Telegraph
N
E
T
H
E
R
M
O
S
T
More clues leading to the result NETHERMOST
- Bottom of flask in pocket
- Clear kind of flask stowed inside, as far down as possible
- . Extremely low number returned drinking flask
- The monster’s wobbly bottom
- Flask placed in bag at the bottom
- Lowest profit involving insulated flask
- Empty beverage container in Northwest Territories, deepest down
- a Bottom pocket filled by flask
- Lowest trap catching vacuum flask
Buddy explains!

The straight part
We know that "at the bottom" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case at the bottom = nethermost.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 NETHERMOST mean?
NETHERMOST adjective- Farthest down; lowest.