To Agree

1. (intransitive) To harmonize in opinion, statement, or action; to be in unison or concord; to be or become united or consistent; to concur.
2. (intransitive) To yield assent; to accede;—followed by to.
3. (transitive, Britain, Ireland) To yield assent to; to approve.
4. (intransitive) To make a stipulation by way of settling differences or determining a price; to exchange promises; to come to terms or to a common resolve; to promise.
5. (intransitive) To be conformable; to resemble; to coincide; to correspond.
6. (intransitive, now always with with) To suit or be adapted in its effects; to do well.
7. (intransitive, grammar) To correspond to (another word) in a grammatical category, such as gender, number, case, or person.
8. (intransitive, law) To consent to a contract or to an element of a contract.

This is a catenative verb that takes the to infinitive.

The transitive usage could be considered as just an omission of to or upon.

US and Canadian English do not use the transitive form. Thus "they agreed on a price" or "they agreed to the conditions" are used in North America but not "they agreed a price" or "they agreed the conditions".

(harmonize in opinion): concur, harmonize

(yield assent): accede, come around, give way; assent

(yield assent to): approve, set

(come to terms or to a common resolve): bargain, deal, engage

(be conformable): coincide, correspond, match, resemble

(do well): fit, suit

(grammar):

(law):

disagree