The most common and most likely answer to this crossword clue is the 8 letter word PLASTRON
I've seen this crossword clue in The Guardian
P
L
A
S
T
R
O
N
More clues leading to the result PLASTRON
Buddy explains!
The straight part
We know that "part of theirs?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of theirs? = plastron.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 PLASTRON mean?
PLASTRON noun- The nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace.
- A half-jacket worn under the jacket for padding or for safety.
- A man's shirt-bosom.
- An ornamental front panel on a woman's bodice.
- A breastplate.
- A film of air trapped by specialized hairs against the body of an aquatic insect, and which acts as an external gill.