A lot people use "agreed" as an interjection, especially while writing comments in blogs, forums, and other online platforms. This use is also mentioned by different English dictionaries (e.g. Collins), but I don't know whether it can be used in a more formal setting than an online forum.
I'm also curious as to its actual meaning.
Is it a shorthand of I have agreed? If so, is the present perfect used (albeit in an abbreviated form) to describe an action that was completed in a very recent past?
Or is it a shortand of I am agreed? I sometimes find this expression, although in a different setting than "agreed", but I'm not sure it is correct.
Or is it something else entirely? I've tried searching on the Internet, but I haven't found an answer so far.
Best Answer
When you use "Agreed" as an interjection, it is equivalent to "I agree." It is short for the much more formal "It is agreed."
One way you typically see this done is when speakers are setting the ground rules (or baseline assumptions) before beginning a discussion where there may be some disagreement.
This likely stems from a more formal era where you were making an oral contract with somebody, and the first speaker declares the terms of the contract, and the second speaker is accepting the terms of the contract. "It is agreed that we will proceed the way we have discussed." Over time this has just been shortened to "Agreed" which then morphed into a simple way of showing agreement.