Expelliarmus is typically used to disarm an opponent of his/her wand. Could it be used to disarm someone of another type of weapon, such as a Basilisk fang, a phial of a dangerous potion, a Venomous Tentacula plant, or even a knife (Morphin Gaunt carried a knife, as did Bellatrix Lestrange)? Are there any instances in canon of Expelliarmus being used to disarm a person of any object other than a wand?
Yes, the spell causes whatever is held by the target to be knocked away. It can even be used to drive an opponent back or knock them unconscious if they have no weapon.
Expelliarmus: Considering possible spell word origins: from Latin expellere, from ex- "out" + pellere "to drive" + arma "weapon" meaning in a direct translation: "to drive out weapons"
From the Harry Potter Wikia:
Canon examples include:
A duel between Professor Snape and Professor Lockhart:
Professor Lockhart was knocked from his feet AND disarmed.
Here is a reference from the text of Chamber of Secrets of the spell being used to remove an object from a target's hand, in this case, Tom Riddle's diary from Malfoy.
The spell was able to remove the diary from Malfoy's hand, implying the spell is not limited to wands OR weapons. Anything can be removed from the hands of the target.
Here is canon movie footage showing the use of the spell both in disarming and knocking down opponents.
This doesn't directly answer your precise question, but we know that Expelliarmus can act on things OTHER than wands. Specifically, on Harry himself.
More specifically, at the very end of the Third Task in "Goblet of Fire", Harry used Expelliarmus to cause a spider to drop him.
Side note: did the spider shout the spell or does JKR need some English grammar lessons? :)
I hate starting answers with "I could find nothing canonical", but here I go again.
My wife asked years ago, "Why don't they just shoot Voldemort?" and I've seen dozens of posts on the same question, but no answer from a reliable source.
All I've found is people stating that Harry couldn't have used a gun on Voldemort, because Voldemort would simply use Expelliarmus to disarm him. Nothing to back the statement up, it's just stated as if it's obvious (which, of course, it's not).
So, the consensus among the fan base would seem to be "yes, Expelliarmus can be used against any weapon".
I believe the fan base has it right in this case, based on the fact that most spells in the Potterverse are loosely baaed on real words, and this one falls into the same pattern. It's a combination of "expel arms", which is exactly what it does.
In other contexts, a wand is a tool, but in the context of a Wizard's Duel, a wand is a weapon. Expelliarmus expels the arms (as in weapons, not body parts) from the hand of the opponent.
If it were specific to wands, I think the spell would be something like "ejecto wandus". (I know that last was made up, but it sounded funnier than "Accio, Voldemort's Wand!")
Of course, that's not canonical, but again, I just couldn't find a direct quote from JKR. I'm very surprised it hasn't been asked in an interview.
Expelliarmus has been used in one other case as part of a weapon. That would be in the Doctor Who episode "The Shakespeare Code". The tenth Doctor along with Martha Jones on her first trip in the Tardis visit Shakespeare to see a play in good ol' England. In the course of the episode they end up (of course) saving the world from the Carionite witches. A part of the only spell of words that would break the impending Carionite doom, is the word Expelliarmus. The actual wordings are as follows ::
"Close up this din of hateful dire decay. Decomposition of your witches plot. You thieve my brains, consider me your toy — my doted Doctor tells me I am not! Foul Carrionites festers, cease your show! Between the points 761390.. Banish thy, antiqueascas, I sing to thee.. EXPELLIARMUS !!!! "
If you LOVE the Doctor Who connection with Shakespeare and good ol' J.K, do up vote the answer.