The most common and most likely answer to this crossword clue is the 6 plus 4 letter word COLLAR BONE
I've seen this crossword clue in The Guardian
C
O
L
L
A
R
B
O
N
E
Buddy explains!
The straight part
We know that "part of upper body" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of upper body = collar bone.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 COLLAR BONE mean?
COLLAR BONE noun- The bone joining the shoulder and the breastbone.