This is the 8432nd most frequent Turkish word.
onca
"As much as that" or "so many/much."
Here, 'onca' denotes 'many' or 'a considerable number of' books, emphasizing the quantity.
Onca kitabı aynı anda nasıl okudu?
How did he read all those books at once?
In this usage, 'onca' refers to 'many' or 'numerous' problems, indicating a large amount to deal with.
Onca sorunla nasıl başa çıkıyorsun?
How do you cope with all those problems?
Here, 'onca' signifies 'so much' or 'a great amount of' effort, stressing the substantial effort put in.