Entry 1 sense Webster, 1913 labourious · IPA 01 adj. characterized by toilsome effort; same as laborious; -- British spelling. 1. characterized by toilsome effort; same as laborious; -- British spelling.[Chiefly Brit.] See: laborious Syn. arduous, backbreaking, back-breaking, grueling, gruelling, hard, heavy, laborious, punishing, slavish, strenuous, toilsome.