defter

/ defter /

Cases

SingularPluralWhen to use it
nominative defter the exercise book defterle the exercise books the plain dictionary form — the doer of the sentence
genitive defterni the exercise book's defterleni the exercise books' the owner — whose it is
accusative defterni the exercise book (as the object) defterleni the exercise books (as the object) a specific, known object — whom or what
dative defterge to the exercise book defterlege to the exercise books direction or recipient — to where, to whom
locative defterde at / in the exercise book defterlede at / in the exercise books where it is; also having — mende bar, "I have it"
ablative defterden from the exercise book defterleden from the exercise books where it comes from; also "than" when comparing

The endings are the same ones the pronouns wear — that page explains when each case is used.

With an owner

One ownedSeveral owned
my defterim my exercise book defterlerim my exercise books
your defteriŋ your exercise book defterleriŋ your exercise books
his / her defteri his / her exercise book defterleri his / her exercise books
our defteribiz our exercise book defterleribiz our exercise books
you all's defterigiz you all's exercise book defterlerigiz you all's exercise books
their defterleri their exercise book defterleri their exercise books

The overlap in the last rows is real, not a mistake: defterleri can mean "his / her exercise books", "their exercise book", or "their exercise books" — context decides.