This is the 71st most frequent Greek word.
πρώτο
"Πρώτο" means "first" in English.
'πρώτο' is used as an adjective modifying 'βιβλίο' to indicate its position as the initial item in a sequence.
Το πρώτο βιβλίο που διάβασα ήταν πολύ ενδιαφέρον.
The first book I read was very interesting.
'πρώτο' is used as an adverb to denote the rank of the subject in arriving at the location.
Έφτασα πρώτο στον προορισμό.
I arrived first at the destination.
'πρώτη' is the feminine singular form of 'πρώτο', agreeing with 'μέρα' which is feminine, to indicate its ordinal position.