(the possessive case of whoever used as an adjective)
Whosever wagon this is, get it out of here. Whosever is this ridiculous hat?
2.
the one or ones belonging to whomever
Whosever will win, do you think?
Word origin
[1730–40; whose + ever]This word is first recorded in the period 1730–40. Other words that entered Englishat around the same time include: bronze, chenille, maximum, optimism, swipe