Duodecimvirate is a word that is rarely used in contemporary English, and as such, finding synonyms for it may be a slightly difficult task. However, there are certain phrases and words that could serve as substitutes for it. One possible replacement is 'twelve-member commission,' which would convey a similar sense of a group of twelve people with authority or power. 'Council of Twelve' is another phrase that could be used, as is 'committee of twelve.' 'Dozen authority' and 'twelve-member team' are other potential synonym options. Ultimately, the choice of synonym would depend on the context in which the term is being used and the specific connotations it is meant to evoke.