The Greek word for "aunt" is "theia." Sometimes the spellings "thia" or "thea" are used because of confusion on translating the Greek alphabet to the Roman alphabet used to write English.
"Theitsa" is an affectionate way to refer to one's aunt in Greece; it translates to "auntie." The word for uncle is "theios," or "thios"; both are often pronounced with a silent S. When addressing an aunt or uncle, it is proper to use "theia" or "theios" followed by the person's first name. As in English, the titles "theia" and "theios" are frequently used by children when talking to close friends of the family who are not actual relatives.