REF: words with two "u"'s

[Mark Thomas Frank <tomatoes@IX.NETCOM.COM>]

Hello all!
    This is a request from my dad, recently retired, and beginning to
fill his time with lots of thinking.  He knows of two words in the
English language that have two "u"s , but is pretty sure that there is
another one.  The ones he knows are "vacuum" and "continuum".  The
third he can't remember may have something to do with insects or
biology or one of the other sciences.  No rush on this, but if anyone
knows the word (or words) or can lead me to a source, I would
appreciate it.

Thanks!

Cathy Frank
Gibson Island Country School
Pasadena  MD

tomatoes@ix.netcom.com