'gruelling' definitions:

Definition of 'gruelling'

From: WordNet
adjective
Characterized by effort to the point of exhaustion; especially physical effort; "worked their arduous way up the mining valley"; "a grueling campaign"; "hard labor"; "heavy work"; "heavy going"; "spent many laborious hours on the project"; "set a punishing pace" [syn: arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome]

Definition of 'gruelling'

From: GCIDE
  • grueling \grueling\, gruelling \gruelling\adj.
  • 1. characterized by toilsome effort; requiring extreme physical or mental effort; as, a grueling campaign.
  • Syn: arduous, backbreaking, back-breaking, exhausting, gruelling, hard, heavy, laborious, labourious, punishing, slavish, strenuous, toilsome. [WordNet 1.5]