1. exhausting Arduous (L. arduus, steep) signifies primarily so steep and lofty as to be difficult of ascent, and hence applies to that which involves great and sustained exertion and ordinarily for a lofty ai Synonyms: difficult, arduous, hard, onerous, toilsome, exhausting, laborious, severe, trying Antonyms: easy, facile, light, pleasant, slight, trifling, trivial