harmon- +

(Greek > Latin: a fitting together, joining, proportion, concord, agreement, musical harmony)

harmonious
1. Marked by agreement in feeling, attitude, or action: "It was a harmonious group."
2. Forming a pleasingly consistent whole; congruous: "The room had such harmonious colors in its decor."
3. Exhibiting accord in feelings or actions.
4. Having component elements pleasingly or appropriately combined.
5. Pleasant to the ear; tuneful; melodious.
harmoniously
1. In a harmonious manner.
2. Exhibiting accord in feeling or action.
3. Having component elements pleasingly or appropriately combined:
harmoniousness
1. The quality of sounding harmonious.

A simultaneous combination of sounds conventionally regarded as harmonious or pleasing.

2. Compatibility in opinion and action; agreement; accord; harmonious relations.
harmoniphon, harmoniphone
An obsolete wind instrument with a keyboard, in which the sound, which resembled the oboe, was produced by the vibration of thin metallic plates, acted upon by blowing through a tube.
harmonist
1. Someone who is skilled in creating musical harmony; a musical composer.
2. Someone who understands the principles of harmony or is skillful in applying them in composition.
harmonium
1. An organ in which a pair of bellows operated by the player's feet blow air into the reeds to produce musical sound.
2. An organ-like keyboard instrument that produces tones with free metal reeds actuated by air forced from a bellows.
harmonizable (adjective)
1. Capable of being made harmonious or consistent.
2. The ability to bring into harmony, accord, or agreement.
harmonization, harmonisation
1. A piece of harmonized music.
2. Singing in harmony.
3. In international law, the process whereby different countries adopt the same laws.
4. The changing of government regulations and practices, as a result of an international agreement, to make those of different countries the same or more compatible.

For example, with tariffs, this means making tariff rates more similar across industries and/or across countries.

harmonize, harmonise (British); harmonized, harmonised
1. To bring into harmony, accord, or agreement: "He was advised to harmonize his views with his new job."
2. To accompany one's music with appropriate harmony.
3. To be in agreement in action, sense, or feeling: "Although the teachers had a multitude of approaches, they were able to harmonize their educational objectives."
4. To sing in harmony; that is, to bring into consonance, harmony, or accord while making music or singing.
harmonizer
1. A mediator who brings one thing into harmonious agreement with others.
2. A musician who sings or plays in harmony.
3. Someone who brings others together or who reconciles others.
harmonizing
1. To bring or to come into agreement or harmony.
2. To provide musical harmony for (a melody); to sing or to play in harmony.
3. To be in agreement; to be harmonious.
4. To bring into consonance or to relate harmoniously.
harmonometer
An instrument for measuring the harmonic relations of sounds.

It is often a monochord furnished with movable bridges.

harmony
1. Working or living together smoothly.
2. Agreement in feelings or opinions; accord; such as, to live in harmony.
3. A pleasing combination of elements in a whole: color harmony; the order and harmony of the universe.
4. In music, the study of the structure, progression, and relation of chords or the simultaneous combinations of notes in a chord.
5. A combination of sounds considered pleasing to the ear.
6. Etymology: from about 1380, armonye, "concord of sounds, music, melody; borrowed from Old French armonie, harmonie, from Latin harmonia, from Greek harmonia, "joining, joint, agreement, concord of sounds.

Related to harmos, "joint". It is also etymologically connected to "arm" from Greek arthron. "a joint" and Latin armus, "shoulder".

—Based on information from Barnhart Dictionary of Etymology
inharmonic
1. Not harmonic; discordant.
2. Lacking harmony.
inharmonious
1. Lacking harmony or sounding unpleasant.
2. Characterized by disagreement and conflict.
3. Not matching in color or style.