Merriam-Webster's Collegiate Dictionary:
nimbyism
nimh
nimiety
niminy-piminy
nimitz
nimrod
nimrud
nin
nincompoop
nincompoopery
nine
nine day wonder
nine days' wonder
nine-to-fiver
ninefold
ninepin
nineteen
nineteenth
ninetieth
ninety
nineveh
ning-po
ningbo
ninghsia
ninghsia, ningsia
ninghsien
ningsia
ningsia hui
ningxia huizu
ninhydrin
ninja
ninny
ninnyhammer
ninon
ninth
ninth cranial nerve
ninus
niobate
niobe
niobium
niobrara
niort
nip
nip and tuck
nip-up
nipa
nipa palm
nipigon, lake
nipissing, lake
nipper
nippily
nippiness
nipping
nippingly
nipple
nippled
nippon
nipponese
nippur
nippy
nirvana
nirvanic
nis
nisan
nisei
nish
nishinomiya
nisi
nissen hut
nist
nisus
nit
nit-picking
nite
niter
niter?i
niterie
nitery
nitid
nitinol
nitpick
nitpicker
nitpicky
nitr-
nitra
nitrate
nitrate of soda
nitration
nitrator
nitre
nitric acid
nitric oxide
nitride
nitrification
nitrifier
nitrifying
nitrifying bacteria
