adamantly

noun

1. in ancient times, a hard stone or substance that was supposedly unbreakable
2. Old Poet. unbreakable hardness

Origin: ME & OFr < L adamas (gen. adamantis), the hardest metal < Gr adamas (gen. adamantos) < a-, not + daman, to subdue: see tame

adjective

1. too hard to be broken
2. not giving in or relenting; unyielding