His steadfast commitment to the project never wavered.
Synonyms for steadfast
reliable
loyal
unwavering
Antonyms for steadfast
wavering
unreliable
fickle
Practice steadfast on real SAT questions
Vocabulary like steadfast appears on the Digital SAT in Words-in-Context questions, where you choose the word that fits a passage's meaning and tone. You can also drill this word with vocabulary flashcards.