(obsolete) The letter fita (Russian фита́(fitá)) or ѳита́(fitá)). A consonantal letter intended to represent the Greek phoneme /θ/, which was approximated in Russian by /f/. Replaced by the letter ф(f) in the spelling reform of 1917.
This letter was used in words of Greek origin in cases where Russian /f/ derived from Greek θ(th) rather than φ(ph). For example, орѳогра́фія(orfográfija, “orthography”), Ѳивы(Fivy, “Thebes”), etc.
In some words the pronunciation had changed to /t/ under French and German influence. These were accordingly replaced with т(t) instead of ф(f).