Similar word to wellestablished:

absolute, complete, confirmed, congenital, deep-down, deep-dyed, deep-rooted, deep-seated, deeply ingrained, die-hard, entrenched, fixed, full-fledged, genuine, hardened, infixed, ingrained, instilled, long-standing, out and out, thorough, thoroughgoing, through and through, to the core, to the core, true, unchangeable, uncompromising, utter, well-established