The Collaborative International Dictionary
labourious
labourious \labourious\ adj. 1. characterized by toilsome effort; same as laborious; -- British spelling. [Chiefly Brit.]
Syn: arduous, backbreaking, back-breaking, grueling, gruelling, hard, heavy, laborious, punishing, slavish, strenuous, toilsome.
Wiktionary
labourious
a. (lb en nonstandard) (alternative form of from=UK laborious English)