Real Dictionary

koppa in American English
noun: a letter (Ϙ,ϙ) of some early Greek alphabets, occurring between pi and rho and equivalent to Latin Q: later superseded by kappa except for its use as a numeral for 90

koppa in British English
noun: a consonantal letter in the Greek alphabet pronounced like kappa (K) with the point of articulation further back in the throat. It became obsolete in classical (Attic) Greek orthography, but was passed on to the Romans who incorporated it into their alpha