firm, steadfast, steady, stiff, unbendable, unfaltering, unshakable, unwavering -- (marked by firm determination or resolution; not shakable; "firm convictions"; "a firm mouth"; "steadfast resolve"; "a man of unbendable perseverence"; "unwavering loyalty")
level, unwavering -- (not showing abrupt variations; "spoke in a level voice"; "she gave him a level look"- Louis Auchincloss)
(TTS Sound)
