strenuous
[adjective]
Synonyms: demanding, arduous, hard, laborious, taxing, tough, uphill

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Antonyms: effortless
Contrasted words: comfortable, cushy, light, unburdensome
Related Idioms: a long hard pull, an uphill climb, tough going
Related Words: breathless, energy-consuming, mean, wicked, Herculean

[TahlilGaran] English Synonym Dictionary ▲

stren‧u‧ous /ˈstrenjuəs/ adjective
[Date: 1600-1700; Language: Latin; Origin: strenuus]

1. needing a lot of effort or strength:
a strenuous climb
The doctor advised Ken to avoid strenuous exercise.

2. active and determined:
Sherry’s been making a strenuous effort to lose weight.
—strenuously adverb:
Barrett strenuously denied rumors that he would resign.

[TahlilGaran] Dictionary of Contemporary English ▲