Θείος-θεία-θείο (3 genders) means divine. The root of the word θείος is Θεός (God).
Θείος/θεία also mean uncle/aunt.
"Θεία Λειτουργία" means "Divine Liturgy", Mass. I assume the capitalization is just to make the title stand out.
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.