Both principal and principle come from the same root word in Latin, primus, or prime. The two words are linked, which accounts for their distinct but similar meanings.
principal和principle都來(lái)自于同一拉丁語(yǔ)詞根，primus或prime。這兩個(gè)單詞雖然不同但相似的含義使得這它們常被聯(lián)系起來(lái)。

Principal

Principal has two meanings, one as an adjective and the other as a noun. However, they have the same pattern: they mean something or someone that is a leader, the first, and/or the most important.
Principal有兩個(gè)意思，一個(gè)是作為形容詞，另一個(gè)是作為名詞。這兩個(gè)單詞盡管詞性不同，卻有相同含義：皆為某事或某人是主導(dǎo)/領(lǐng)導(dǎo)，第一個(gè)或最重要的。

Noun: the head, chief, or leader; the leader of a school; the initial sum of an investment
名詞詞性：首腦、首席或領(lǐng)導(dǎo)；學(xué)校的領(lǐng)導(dǎo)；投資的初始金額

Adjective: the most important, the chief; referring to the initial sum of an investment
形容詞詞性：最重要的，主要的；指投資的初始金額。

Principle

Principle is always a noun, unless the word is in a different form.
Principe除變形外只為名詞。

Noun: A truth or idea that serves as the foundation for something, such as a belief, behavior, or moral code; an accepted rule for conduct
名詞詞性：作為某事基礎(chǔ)的真理或想法依據(jù)，如信仰、行為或道德準(zhǔn)則；公認(rèn)的行為準(zhǔn)則

Principled is the adjective form of principle. It simply describes something (a person, moral code, etc.) that is founded on principles.
Principled是principle的形容詞形式。只用來(lái)描述基于原則的事物（如，人，道德準(zhǔn)則等）。