What does Siya mean?
A regional and poetic short form of सीता (Sītā), the heroine of the Ramayana, whose name means 'furrow' (she was found in a ploughed field). Siya is widely used in Hindi devotional usage (as in 'Siya-Ram').
What does Diya mean?
From the Hindi दीया (diyā), 'an oil lamp', descended from the Sanskrit dīpa ('lamp, light'). A genuine, everyday Hindi word evoking the lamps of Diwali.