"Nomenclature".
OED has two pronunciations for it:
nə(ʊ)ˈmɛŋklətʃə (nuh-men-cla-cher)
and
ˈnəʊmənˌkleɪtʃə (nomen-clay-cher)
I use the former of the two, albeit without any real reason.
Which is the most-oft used and are there geographical preferences?