The adjective adamant has no traditional corresponding noun, so when we want to refer to the state or quality of being adamant, we usually have to add a noun for the adjective to modify—e.g., adamant insistence, adamant belief, adamant stand. But there is an alternative, albeit a risky one—the noun adamance. Coined in the early 20th century, the word is new enough to have earned a spot in some dictionaries (and our spell check does not say it’s wrong), but as it is a new and not very well-established word, some readers might find it objectionable.
The OED lists an early instance of adamance from 1925, and we can find no earlier examples. Use of the word did not pick up until the 40s and 50s, and it seems to have peaked around 1980 (according to a Google Ngram). While it’s easy to find a few scattered examples of adamance in 21st-century writing, the word is still rare, and we find almost no examples in edited news publications. So whether the word will ever catch on remains in doubt. Use it if you want to be a trailblazer, but it might be best avoided if you’re writing for school or in any other formal context.
Thus the union’s adamance in the bus strike is not so much for the busmen’s benefit as it is a go-the-limit device for convincing the subway workers that their union is strong. [Business Week (1941)]
Mr. Dole’s remarks were his strongest attack yet on the Administration’s adamance on big increases in the military budget. [New York Times (1985)]
It is a remarkable video — both for the sheer number of Kerry’s lurches on the war and because of the adamance with which he expresses incompatible views. [Boston Globe (2004)]
Despite his initial adamance that he got the grammar right by including the indefinite article, Armstrong acknowledged at a 30-year anniversary event in 1999 that he couldn’t hear himself utter the “a” in the audio recording. [Christian Science Monitor (2012)]