Here’s a fun one, the definitions are mostly contradictory, mostly obsolete and none of it is real anyway. Most excellent.
adamant, n. and a.
1. a. Without identification with any other substance.
2. a. Identified with the diamond. Obs.
b. as the natural opposite of the loadstone. Obs.
3. a. Identified with the loadstone or magnet. Obs.
b. as the natural opposite of the diamond. Obs.
c. fig. A magnet, centre of attraction. Obs.
4. Confusing 3 with 1 or 2. Obs.
B. adj. Unshakeable, inflexible, esp. to be adamant, stubbornly to refuse compliance with requests. (The point at which the n. use passed into adj. is not determinable.)
Hence adamantly adv.