say it: STED-fast-lee
steadfastly is an adverb meaning "with resolute determination". It carries one recorded sense.
with resolute determination
“we firmly believed it”
“you must stand firm”
Definitions, synonyms and semantic relations for steadfastly come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.