out of wit/out of wits

Neither. It is 'out of one's wits'.

http://www.thesaurus.com/browse/out%20of%20wit

But, in the above dictionary, it defines "out of wit" as "beside oneself." I assume the thesaurus is wrong, then?

But, thesaurus defines "out of wit" as "beside oneself." Please clear my confusion...

http://www.thesaurus.com/browse/out%20of%20wit

vdbPlease clear my confusion...

OK, I will.
See definitions: 5, 6, 7 and 8

http://dictionary.reference.com/browse/wit?s=t

Personally, I have never in my life heard the expression "out of wit."
I have heard expressions like: "He is out of

Hi

I agree with the above, but you can say that, colloquially, with a verb phrase, something like 'run out of' ...

- I'd like to say more about this subject, but I'm afraid I've run out of wit

(Then, it would be singular and it would mean that I've run out of ideas on the subject)

Dave

But that is more an example of the phrasal verb "run out of", not the idiomatic phrase "out of one's wits."
My car ran out of gas.

Yes, you're right Alphecca. Could I have:

- What're we going to do now?

- Don't ask me, I'm plain out of wit

Dunno, maybe I'm grasping at straws

Dave

dave_anongrasping at straws

Now that's a good idiom!

"out of his wits"
"at his wit's end"

Both are true idioms meaning exasperated, upset, frustrated.

I'm out of ideas. (Not an idiom.)

P.S. I like your new avatar!

... and I'm flogging a dead horse. But here's a blog that uses the idiom as I imagined it. Nice photo but, yes, a rare form of words

Best regards, Dave

https://mageowl.wordpress.com/2015/06/16/june-im-out-of-wit-and-humor/

"He was out of wits at the blow."

This is a sentence that appeared as a question in my English test today. Is it correct? In British English or American English or both?