The most common and most likely answer to this crossword clue is the 5 letter word GLUTE
I've seen this crossword clue in The Guardian
G
L
U
T
E
More clues leading to the result GLUTE
Buddy explains!
The straight part
We know that "Contractor in bottom" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case contractor in bottom = glute.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 GLUTE mean?
GLUTE noun- (exercise) A gluteal muscle.