The combination uu occurs rarely in the English language

English language

English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 and, other than continuum, muumuu and vacuum, in words which are unfamiliar or archaic. With the exception of Muumuu (Hawaiian) and (Welt)anschauung (German), they derive from Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 roots. It is highly debatable as to whether unuunilium should count, as it was firstly renamed to Ununilium, which in turn was renamed to the current Darmstadtium

Darmstadtium

Darmstadtium is a chemical element with the symbol Ds and atomic number 110. It is placed as the heaviest member of group 10, but no known isotope is sufficiently stable to allow chemical experiments to confirm its placing in that group...

.

They are as follows:

• Anschauung
• Carduus
  Carduus
  Carduus is a genus of about 90 species of thistles in the family Asteraceae, native to Europe, Asia and Africa. Carduus is Latin for a thistle....
  
  
• Continuum (also Continuüm)
• Duumvir
• Equus
• Fatuus
• Menstruum (also Menstruüm)
• Muumuu
  Muumuu
  The muumuu or muumuu is a loose dress of Hawaiian origin that hangs from the shoulder. Like the Aloha shirt, muumuu exports are often brilliantly colored with floral patterns of generic Polynesian motifs. Muumuu for local Hawaiian residents are more subdued in tone...
  
  
• Mutuum
• Nuuk
  Nuuk
  Nuuk, is the capital of Greenland, the northernmost capital in North America and the largest city in Greenland. Located in the Nuup Kangerlua fjord, the city lies on the eastern shore of the Labrador Sea and on the west coast of Sermersooq. Nuuk is the largest cultural and economic center in...
  
  
• Obliquus
• Residuum (also Residuüm)
• Triduum (also Triduüm)
• Vacuum
  Vacuum
  In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
  
  
• Weltanschauung