One of the mysteries of the English language finally explained.
Synonyms of arduous in English:
arduous
See definition of arduous
adjective
1‘she was now faced with an arduous journey into a remote country’
SYNONYMS
onerous, taxing, difficult, hard, heavy, laborious, burdensome, strenuous, vigorous, back-breaking, stiff, uphill, relentless, Herculean
demanding, trying, tough, challenging, formidable, exacting
exhausting, wearying, fatiguing, tiring, punishing, gruelling, grinding
intolerable, unbearable, murderous, harrowing
informal killing, no picnic
British informal knackering
archaic toilsome
rare exigent
ANTONYMS
easy, effortless