'Sa-wat-dee-ka' means hello as spoken by a female in Thai.
'Sa-wat' means blessing or good fortune.
'Dee' means good, fine, nice etc.
'Ka' is a phrase ending that increases 'politeness', spoken on its own 'Ka' is also how a female says 'yes'.
'Sa-wat-dee-khrap' means hello as spoken by a male, and 'Khrap' is the male equivalent of 'Ka'