-ίτης

• -ῖτῐς (-îtĭs) — feminine

Back-formation from a rebracketing of πολῑ́της (polī́tēs, πόλῐς (pólĭs, “city”) +‎ -της (-tēs, demonym suffix)), by reanalysing it as πόλ- (pól-) +‎ -ῑ́της (-ī́tēs).

-ῑ́της • (-ī́tēs) m (genitive -ῑ́του); first declension

1. Suffix forming a masculine noun: one connected to, a member of; one from a particular place (demonym)

• Originally formed generic adjectives, such as ὁπλῑ́της (hoplī́tēs, “hoplite”, from ὅπλον (hóplon, “large shield”), literally “one with armour”); πολῑ́της (polī́tēs, “citizen”, from πόλῐς (pólĭs, “city”), literally “one from the city”) etc.
• By the Hellenistic period, both masculine -ῑ́της (-ī́tēs) and feminine -ῖτις (-îtis) became very productive in forming technical terms for products, diseases, minerals and gems (adjectives with elliptic λίθος (líthos, “stone”)), ethnic designations and Biblical tribal names. These technical uses survive in modern languages in Greek loanwords for diseases (in -itis), for minerals (in -ite) and for nations, tribes or religious sects (plurals in -ites), partly also in common nouns such as hermit.

• Latin: -ītēs

• Smyth, Herbert Weir (1920), “Part III: Formation of Words”, in A Greek grammar for colleges, Cambridge: American Book Company, § 843