The building may be used for whatsoever purpose the tenant desires.
adverb
(chiefly in the negative) In any way; at all; whatever.
He gave me no answer whatsoever.
pronoun
(archaic or literary) Whatever.
Whatsoever you seek, you will find.
c. 1613–1621, Francis Bacon, The judicial charge upon the commission of Oyer and Terminer held for the verge of the Court
[…] I must require you to use diligence in presenting especially those purloinings and imbezlements, which are of plate, vessel, or whatsoever within the King's house.