I have heard this word
pronounced two different ways, and both equally
common. In my experience, it seems that
computer scientists like to pronounce it "TOO - pul", whereas
mathematicians like to pronounce it "TUH - pul".
According to
Webster, the former is correct.
TUPLE is also the name of a
programming language/
development environment, a
parallel LISP based on
KCL. It stands for "
Toyohashi University Parallel Lisp Environment". (This last definition I discovered at
Dictionary.com)