What is another word for "hard"?

Roget's Thesaurus (1911) lists these synonyms for "hard": acerb, acescent, acetic, acetose, acetous, acid, acidify, acidity, acidulate, acidulous, adamant, adamantean, adamantine, adder, adventure, agent, aim, aloof, alum, ambiguity, anaesthesia, anaesthetic, anaesthetize, anal, and, applicant, aspirant, attempt, bagman, beetle, beggar, being, belief, believe, benefit, benumb, best, bidder, block, blunt.