Vacuum is not the only English word containing a double u (i.e. uu).
There exists another non-related term with the said feature, used both in mathematics and in music.

Find it and others (there are several words, mostly derived from Latin).

(In reply to words by Charlie)

carduus - a thistle
individuum - an indivisible entity; (archaic) an individual
lituus - (Roman antiquity) a type of curved trumpet
mutuum - a contract for the loan of consumable goods to be repaid in kind
obliquus - a structure having an oblique course or direction
paramenstruum - the four days before the first four days of mentstuation
ultravacuum - an extremely high-level of vacuum; a device for creating such
vacuumes - third-person simple present of vacuum

And the anglicized plurals of the borrowed Latin words:
carduuses, individuums, lituuses, mutuums,
paramentstruums, ultravacuums 

Posted by Dej Mar on 2013-06-01 00:11:20