Formidable
Formidable adjective - Requiring considerable physical or mental effort.
Usage example: running a marathon is a formidable undertaking
Heavy is a synonym for formidable in onerous topic. In some cases you can use "Heavy" instead an adjective "Formidable".
Nearby Word: formidably
Heavy
Heavy adjective - Requiring considerable physical or mental effort.
Usage example: until we find our groove, it's going to be heavy sledding on this project
Formidable is a synonym for heavy in difficult topic. Sometimes you can use "Formidable" instead an adjective "Heavy", if it concerns topics such as onerous.
Mutual synonyms
Both words in one sentence
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It is appropriate to think that Men are far more formidable as enemies to Orcs as heavy cavalry than Elves - even the Noldor - as infantry.
Source: Call That a Formation? - The French Char B1-bis heavy tanks in WWII were pretty damn formidable, despite being based on, by then, an outdated design paradigm.
Source: Curb Stomp Battle / Real Life -
Earn Your Happy Ending: Yuu's formidable task of finding every ability user in the world in episode 13 really takes a heavy toll on his sanity.
Source: Anime / Charlotte
Cite this Source
Heavy and Formidable. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/formidable/heavy
Formidable & Heavy. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/formidable/heavy>.
Heavy or Formidable. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/formidable/heavy.
Google Ngram Viewer shows how "formidable" and "heavy" have occurred on timeline