MockingbirdGirl is quite right. The -re spelling comes from the word's classical (ancient Greek) origin - which is why both the British and the French (and Spaniards, Italians, and Slavs) use it.
The -er spelling actually came into American English through academia, where it was derived from the German. Apparently Saxons had trouble with that Greek/Latin double consonant (Theatron, Theatrum), so they inserted a vowel.
But we're not German academics (most of us aren't, anyway), so there's no reason for Americans to use any but the classic spelling. |