The most common and most likely answer to this crossword clue is the 5 letter word RICIN
R
I
C
I
N
More clues leading to the result RICIN
- Poison from old chemical company conveyed by sailors
- Poisonous stuff in turmeric, I noted
- Part of Santorini circle that’s thrust up toxic stuff
- Involved in pricing product of castor oil seeds
- Toxic substance secreted by prehistoric insects
- Poison murderer finally added to top of cake – not good!
- Tim endlessly popular? That’s toxic!
- Banks avoid costing toxic compound
- Toxic stuff, dose of arsenic irrationally knocked back
- Toxic stuff used in twisted crime, we hear
Buddy explains!

The straight part
We know that "bioweapon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bioweapon = ricin.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 RICIN mean?
RICIN noun- An extremely toxic protein extracted from the castor bean.