Faithful, loyal, true, constant, staunch, steadfast, resolute are comparable when meaning firm in adherence to the person, the country, or the cause to whom or to which one is bound by duty or promise.
Faithful in its most common sense implies firm and unswerving adherence to a person or thing to whom or to which one is united by some tie (as marriage, friendship, political allegiance, gratitude, or honor) or to the oath, pledge, or promise made when one has accepted a position, an office, or an obligation.
The term is also used when only firm adherence to actuality or reality (as in representation or portrayal) is implied; it then comes close to accurate or exact in meaning.
Loyal implies faithfulness to one’s pledged word or continued allegiance to the leader, the country, the institution, or the principles to which one feels oneself morally bound; the term suggests not only adherence but resistance to being lured or persuaded away from that adherence.
True (see also REAL ) is somewhat stronger than loyal and faithful in stressing a personal or emotional quality as well as steadiness in one’s allegiance, devotion, or fidelity.
Constant also stresses firmness or steadiness in attachment, devotion, or allegiance, but it carries a weaker implication of strict adherence to one’s vows, pledges, or obligations. Consequently it often implies a state of mind that is the opposite of fickleness rather than a course of action that is the opposite of unfaithfulness and disloyalty.
Staunch carries far more strongly than loyal an implication of one’s unwillingness to be turned aside from those to whom one owes allegiance or to whom one has pledged one’s troth or from an institution (as a church or political party) to which by conviction one belongs. From its earliest and still current nautical sense of being watertight and sound it retains a suggestion of an inherent imperviousness to all influences that would weaken one’s loyalty or steadiness in faith.
Steadfast so stresses unwavering or unswerving adherence that the term is applicable not only to persons but to things that maintain a steady course or an unchanging quality or character. However its most usual application is to persons or their attachments.
Resolute implies steadfastness and, often, staunchness, but it throws the emphasis upon a determination which cannot be broken down as a quality of character and may suggest firm adherence to one’s own purposes or ends rather than to those of others.