10
hard(adjective, tough, severe, evil, difficulty)
10
awful(adjective, great, tough, terrible, fear)
10
burdensome(adjective, tough, severe, difficult, heavy)
10
daunting(adjective, tough, awful, horrible, grand)
10
fearsome(adjective, awful, wonderful, fear, grand)
10
menacing(adjective, bad, tough, severe, unpleasant)
10
strenuous(adjective, tough, severe, rough, difficult)
9
alarming(adjective, bad, awful, heavy, fear)
9
frightening(adjective, awful, terrible, wonderful, disgusting)
9
awe-inspiring(adjective, awful, wonderful, fear, amazing)
9
horrific(adjective, bad, great, tough, fear)
9
imposing(adjective, tough, awful, wonderful, horrible)
9
rough(adjective, hard, tough, nasty, difficult)
9
shocking(adjective, appearance, bad, great, unpleasant)
9
terrifying(adjective, tough, awful, wonderful, grand)
8
dread(fear, dreadful)
8
horrible(adjective, great, tough, unpleasant, awful)
8
severe(adjective, appearance, great, tough, difficult)
8
titanic
8
toilsome(adjective, tough, severe, difficulty, difficult)
11 years ago|23k views|share |citing 
APASmart Define. (2015). formidable thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/formidable/thesaurus/synonyms
ChicagoSmart Define. 2015. "formidable thesaurus" https://smartdefine.org/formidable/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2015, formidable thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/formidable/thesaurus/synonyms>.
MLASmart Define. "formidable thesaurus" 17 July 2015. Web. 20 September 2026. <https://smartdefine.org/formidable/thesaurus/synonyms>