Are you sure that's the whole of the definition from the source you took it from? It looks suspiciously like a fragment of the definition on en.oxforddictionaries.com, omitting the part of the definition that is more general.

https://en.oxforddictionaries.com/definition/weapon

Yes. Consider a detailed blueprint for a physical weapon. Or information that make coordinated use of armed forces more efficient. Or blackmailing material.

I think information is likely more analogous to ammunition than to a weapon.

By itself, it is harmless, but when paired with an appropriate device, by a user with malicious intent, it can then be used to cause harm.

As you've specified a weapon must be a thing, then trivially no, by definition.

But certainly information can be used for extortion, or to otherwise coerce people against their will, and maybe that's enough?

> As you've specified a weapon must be a thing, then trivially no

"Information" is a noun, hence it is a "thing".

Furthermore, the 'physical damage' it can inflict is the destruction or manipulation of physical memory cell states.

If you want to have the argument that a "thing" can mean "information" I wish you all the luck in getting a partner that agrees with you. Personally it's both for me, depending on the occasion.

There is no argument, "information" is a "thing", by definition.

So psychological and material harm are irrelevant?