From Longman Dictionary of Contemporary Englishtaskmastertask‧mas‧ter /ˈtɑːskˌmɑːstə $ ˈtæskˌmæstər/ noun → be a hard/stern/tough taskmaster
Examples from the Corpus
taskmaster• The market therefore serves as both information system and taskmaster.• True to his word, he schooled her in horsemanship and was a hard taskmaster.• Freedom is a heavy taskmaster for those awake enough to appreciate it.• No central planner need call, no taskmaster need coerce.• It had been a hard day and the river could be a severe taskmaster at times.• If self-employment is any guide, the dejobbed worker is likely to be a stern taskmaster. 