strict or thorough in the performance of duty

a faithful worker.

true to one's word, promises, vows, etc.

steady in allegiance or affection; loyal; constant

faithful friends.

reliable, trusted, or believed.

adhering or true to fact, a standard, or an original; accurate

a faithful account; a faithful copy.

Obsolete . full of faith; believing.

the faithful,

the believers, esp. members of a Christian church or adherents of Islam.

the body of loyal members of any party or group.

noun

dishonesty , disloyalty , falseness , inconstancy , treachery

noun

adherence , adhesion , allegiance , ardor , attachment , care , constancy , dependability , duty , fealty , fidelity , loyalty , piety , trustworthiness , truth , steadfastness