From BiblePortal Wikipedia

King James Dictionary [1]

FIDEL'ITY, n. L. fidelitas, from fides, faith, fido, to trust. See Faith.

1. Faithfulness careful and exact observance of duty, or performance of obligations. We expect fidelity in a public minister, in an agent or trustee, in a domestic servant, in a friend.

The best security for the fidelity of men, is to make interest coincide with duty.

2. Firm adherence to a person or party with which one is united, or to which one is bound loyalty as the fidelity of subjects to their king or government the fidelity of a tenant or liege to his lord. 3. Observance of the marriage covenant as the fidelity of a husband or wife. 4. Honesty veracity adherence to truth as the fidelity of a witness.

Vine's Expository Dictionary of NT Words [2]

1: Πίστις (Strong'S #4102 — Noun Feminine — pistis — pis'-tis )

"faith, faithfulness," is translated "fidelity" in  Titus 2:10 . See Faith (b).

Webster's Dictionary [3]

(1): ( n.) Faithfulness; adherence to right; careful and exact observance of duty, or discharge of obligations.

(2): ( n.) Adherence to a person or party to which one is bound; loyalty.

(3): ( n.) Adherence to the marriage contract.

(4): ( n.) Adherence to truth; veracity; honesty.

Charles Buck Theological Dictionary [4]

Faithfulness, or the conscientious discharge of those duties of a religious, personal, and relative nature, which we are bound to perform.

See an excellent sermon on the subject in Dr. Erskine's Sermons, vol. 2: p. 304.