The Merriam-Webster dictionary defines a poison in broad terms (noun. A substance that through its chemical action usually kills, injures, or impairs an organism) and venom as (noun. A toxic substance produced by some animals (such as snakes, scorpions, or bees) that is injected into prey or an enemy chiefly by biting or stinging and has an injurious or lethal effect). These definitions have been in common usage, however, they don't adequately encapsulate the intricacies and variation observed within biological toxins.
Recently, scientists have proposed more rigorous definitions (see
2014. Nelson, et al. Biological Reviews 2014(89): 450-465.
) of toxic biological secretions to eliminate the rampant inconsistency and ambiguity while facilitating better communication for such a medically important topic.
The standards and stringency of clarity by which scientists discuss poisons/venoms and the organisms that produce them, should not be held to the general public. The layperson referring to a "poisonous snake" is not wrong and the message is clear.