The dictionary isn’t really your friend there. It’s saying that one meaning of poisonous is “having the properties or effects of poison”, and that a synonym in that sense is venomous. The corresponding definition of venomous has poisonous as a synonym, but in the sense “having a venom-producing gland and able to inflict a poisoned wound” no synonyms are given.
Which of course doesn’t mean you’re wrong, just that you shouldn’t have quoted that dictionary.
Not at all; the two definitions confirm what I said.
The full definition of venomous is:
Bolding mine.
In the broadest usage, venomous simply means “full of poisonous material,” as in Shakespeare’s “Sweet are the uses of adversity, Which, like the toad, ugly and venomous, Wears yet a precious jewel in his head.” (As You Like It, Act II, Scene 1).
While the distinction you mention is sometimes made, it is not a necessary one. It is correct to use poisonous and venomous as synonyms.
What the dictionary lacks is a definition for poisonous as “having a venom-producing gland and able to inflict a poisoned wound”.
Unless you think m-w divided their definition for venomous into two separate meanings for fun, the meaning of venomous that the original nit-pick implies, doesn’t have poisonous as a synonym, and your original quote for the definition for poisonous only has poisonous as synonymous to venomous in the “having the properties or effects of poison”-sense.
It might not be a necessary distinction and using poisonous and venomous as synonyms in all senses may be correct and universal, but saying that the dictionary doesn’t indicate otherwise is obviously wrong.
Why should it? It’s unnecessary to specify all possible meanings of “poisonous.”
Bolding mine.
Sorry, you’re wrong. Of course the platypus is venomous in the sense of injecting its poison/venom. However, to say that for that reason it is not poisonous is incorrect. It is both venomous, in the sense of injecting its poison, and venomous, in the sense of containing venom. It is poisonous in the sense of being harmful; and having the effects of poison (when it injects the venom).
The dictionary indicates that it is possible to make some distinctions; it does not indicate that the original nit-pick was correct.