adjective
1.
Synonyms: hard 6, arduous, difficult, effortful, formidable, laborious, severe, strenuous, toilsome, tough
2.
Synonyms: assiduous , diligent, industrious, sedulous
OPEROSE
Meaning of OPEROSE in English
Merriam Webster. Collegiate thesaurus English vocabulary. Английский энциклопедический словарь тезаурус. 2003