whosever

Determiner

 * 1)  Of whomever; belonging or related to whatever person or persons; whoever's.
 * Whosever property it is, it will be seized.

Pronoun

 * 1)  That of whomever; that which belongs or is related to whatever person or persons; whoever's.
 * Whosever it is, it will be seized.

Usage notes
In everyday language, is used instead.

Etymology 2
From whoever with whose replacing who.

Contraction

 * 1)  whoever is.