mischievous
Pronunciation: /ˈmɪstʃɪvəs/
adjective

Origin:
Middle English: from Anglo-Norman French meschevous, from Old French meschever 'come to an unfortunate end' (see mischief). The early sense was 'unfortunate or calamitous', later 'having harmful effects'; the sense 'playfully troublesome' dates from the late 17th century

Mischievous is a three-syllable word; it should not be pronounced with four syllables, as if it were spelled mischievious /mɪsˈtʃiːvɪəs/.