principally Definition

principal
adj

1. First in rank or importance; chief; main.

Thesaurus: leading, main, chief, primary, foremost, first, cardinal, capital, dominant, controlling, essential, paramount, pre-eminent, key, controlling; Antonym: subordinate, least, lesser, minor.

noun

1. The head of an educational institution.

Thesaurus: chief, director, dean, leader, top dog, headmaster, head teacher, superintendent, master, boss, rector.
2. A leading actor, singer or dancer in a theatrical production.

Thesaurus: star, lead, prima donna.
3. law.
The person on behalf of whom an agent is acting.
4. law.
Someone ultimately responsible for fulfilling an obligation.
5. Someone who commits or participates in a crime.
6. commerce.
The original sum of money on which interest is paid.
7. music.
The leading player of each section of an orchestra.

Derivative: principally
adverb

Chiefly or mainly
Thesaurus: mainly, mostly, primarily, above all, chiefly, especially, particularly, predominantly.

Etymology: 13c: French, from Latin principalis chief, from princeps leader.

Info:

These words are often confused with each other.