Complex sentence: The word "Seimas" comes from a Lithuanian word "Sueiga, suėjimas" (which means gathering or meeting) it is also though that the Polish word "sejm" and Latvian "Saeima" comes from the word "Seimas".
Split into simpler sentences: The word "Seimas" comes from a Lithuanian word "Sueiga, suėjimas", which means gathering or meeting. Tt is also thought that the Polish word "sejm" and Latvian "Saeima" comes from the word "Seimas".