This is the 1632nd most frequent Russian word.
александру
"Александру" is the dative form of the name "Александр" (Alexander) in Russian, meaning "to Alexander."
The word 'Александру' is in the dative case, indicating the indirect object of the verb, to whom the book was given.
Я подарил книгу Александру.
I gave the book to Alexander.
The word 'Александром' is in the instrumental case, showing the means or accompaniment, referring to the person participating in the discussion.
Мы обсуждали идею вместе с Александром.
We discussed the idea with Alexander.
The word 'Александра' is in the genitive case, indicating possession or relation, meaning that the gift is intended for Alexander.