This is the 6753rd most frequent Turkish word.
başkaya
"Başkaya" means "someone or something different or unique."
In this sentence, 'başkaya' conveys 'in addition to the other' emphasizing an additional exception or consideration.
Bu kitabı, diğerlerine ek olarak başkaya yazdım.
I wrote this book in addition to the others.
Here, 'Başkaya' is used as a proper noun, functioning as the subject of the sentence referring to a person's name.
Herkes bahçede eğleniyordu, ancak başkaya neşeli bir şekilde şarkı söylüyordu.
Everyone was enjoying themselves in the garden, but Başkaya was cheerfully singing.
'Başkaya' in this instance serves as a poetic or slightly archaic expression to emphasize hopeless circumstances except for one possibility.