faithful
noun
any loyal and steadfast following
a group of people who adhere to a common faith and habitually attend a given church
adjective
steadfast in affection or allegiance
“years of faithful service”
“faithful employees”
Oppositesunfaithfulmarked by fidelity to an original
“a close translation”
“a faithful copy of the portrait”
Synonymsclosenot having sexual relations with anyone except your husband or wife, or your boyfriend or girlfriend
“he remained faithful to his wife”
Oppositesunfaithful
Source: WordNet 3.1, Princeton University