Origin: 1250–1300; ME
feithful. See faith, -ful 
Related forms: faith⋅ful⋅ly, adverb
faith⋅ful⋅ness, noun
Synonyms:
1, 3. true, devoted, staunch. 3. Faithful, constant, loyal imply qualities of stability, dependability, and devotion. Faithful implies long-continued and steadfast fidelity to whatever one is bound to by a pledge, duty, or obligation: a faithful friend. Constant suggests firmness and steadfastness in attachment: a constant affection. Loyal implies unswerving allegiance to a person, organization, cause, or idea: loyal to one's associates, one's country. 5. precise, exact.
[feyth-fuh