fifth declension noun, and so the plural is not -us, -i but rather -us, -us

If it is 5th declension I think the nominative plural would be apparates but I won't swear. My noun decliner on my machine here at work only goes up to 3rd declension. The genitive singular would be apparatus. Lessee what AHD has to say, if anything useful.

FWIW, it lists the plurals (it has two) as apparatus and apparatuses. When giving the Latin it doesn't use a long u in the -us suffix and I believe the -us in the nominative singular has a long u.

Well, I went here (http://catholic.archives.nd.edu/cgi-bin/lookup.pl?stem=apparat&ending=us) and it looks like it's 4th declension, but the plural would be apparatus.