Since the question seems to regard when somebody does something, I would suppose that you want a verb, so my guess is that your forgotten word is Err, under this definition of the word from the American Dictionary of the English Language (A.D.E.L.) by Noah Webster:
- To mistake; to commit error; to do wrong from ignorance or inattention. Men err in judgment from ignorance, from want of attention to facts, or from previous bias of mind.
Committing error should be cross referenced with the error entry, which starts with the following passage and more directly asserts the criterion of belief in the claim being made:
A wandering or deviation from the truth; a mistake in judgment, by which men assent to or believe what is not true. error may be voluntary, or involuntary. Voluntary, when men neglect or pervert the proper means to inform the mind; involuntary, when the means of judging correctly are not in their power.
And similarly A.D.E.L. shows an false statement can be described with the adjective erroneous:
- Wrong; false; mistaken; not conformable to truth; erring from truth or justice; as an erroneous opinion or judgment.
It also shows that all three of these words are cognate, as they derive from the latin Erro.
The word is particularly common in a few phrases, such as "To err is human" or "err on the side of caution", howevter in these cases it more broadly means to make any sort of mistake, rather than making false claims specifically.
Nevertheless, it can be specifically applied to false claims as well and such usage is extensively demonstrated in* A Relation of the Conference Between William Laud, Late Lord Arc-Bishop of Canturbury and Mr. Fisher the Jesuit By the Command of King James of Ever Blessed Memory with An Answer to Such Exceptions as A.C. Takes Against it* (fourth edition revised 1685)* which includes many uses of the word. This source is especially useful since I presume, at least for the mostpart, the correspondents hold the holiest of men in the Church of Christ as honest people, working hard to determine the most accurate interpretation of holy scripture, and the nature of the question considers the possibility that their consensus is beyond fault.
I have some difficulty selecting a specific passage for the sake of inclusion, but I think this one from what seems to be page 146 is useful.
B. Whether a General Council may err or not is a question of great consequence in the Church of Christ. To say it cannot err, leaves the church not only without remedy against an error once determined, but also without sense that it may need a remedy, and so without care to seek it; which is the misery of the Church of Rome at this day. To say it can err, seems to expose the Members of the Church to an uncertainty, and wavering in the faith; to make unquiet spirits, not only to disrespect former Councils of the Church, but also to slight and contemn whatever it may now determine: Into which error some Opposers of the Church of Rome have fallen. And upon your question, wherein are we nearer to unity, if a Council may err? As if Grounds of Faith may vary at the Racket, and be caft of each fide, as a cunning Hand might lay them.
To briefly address the concerns of people who may have doubt that this usage remains contemporary, I shall also provide a definition written in The Shorter Oxford English Dictionary 5th Edition (©2002)
- Make a wrong judgement; form a wrong opinion; make a mistake, blunder; (of a statement) be incorrect. M.E.
Unlike the first and fifth definitions, this meaning was not marked with the dagger of obsolescence.