yes, it's a text I'm translating from English, but it might be misspelled...? I've found some results on google too, though...

Are you sure "sleight" is the word? It seems very odd without more context. New Oxford American Dictionary sleight | slaɪt | noun literary the use of dexterity or cunning, especially so as to deceive: except by sleight of logic, the two positions cannot be harmonized.

Are you sure 'sleight' is correct? The book was leaning at a slight angle, means it is not vertical.

I don't know about "slight", but an acute angle is less than 90 degrees. The word for greater than 90 is obtuse.