Had to look it up, continuum, but there’s more than three
http://jakubmarian.com/a-complete-list-of-english-words-that-contain-uu-two-us-in-a-row-with-pronunciation/
“menstruum /ˈmɛnstruəm/ (men-stroo-əm), rarely written also “menstruüm”, is an archaic term for a solvent, i.e. a liquid that dissolves a solid.”
I thought that happened monthly?
;)