Wiktionary
thetes
n. (cx historical English) The lowest social class of citizens in ancient Athens.
Wikipedia
Thetes
The thetes (, thêtes, sing. θής, thēs, "serf") were the lowest social class of citizens in ancient Athens after the political reforms of Solon. The thetes were those who were workers for wages, or had less than 200 medimnoi (or their equivalent) as yearly income. This distinction spanned from some time earlier than 594/593 BC until 322 BC.
They had a crucial role in the Athenian navy as rowers.