Synonyms of inflexibly

2 Syllables
stably, firmly
3 Syllables
durably, headstrongly, doggedly, stolidly, mulishly
4 Syllables
unchangeably, unshakeably, tenaciously, bullheadedly, intractably, pigheadedly, resistantly, resolvedly, unyieldingly
5 Syllables
unrelentingly, obdurately, indomitably, unalterably, obstinately, unwaveringly, pertinaciously, contumaciously
6 Syllables
opinionatedly