Well, we're just over halfway =]

nacarat - a bright orange-red colour

nagware - computer software which is free for a trial period and thereafter frequently reminds the user to pay for it (not your partner reminding you that you should really wear that disgusting jumper a relation gav you last Christmas)

nainsook - a fine, soft cotton fabric, originally made in the Indian subcontinent

nesh - Brit. dialect weak, delicate, or feeble (tends to be used in Staffordshire, Yorkshire and midlands)

netizen - a habitual or keen user of the Internet (guilty as charged)

noctambulist - a sleepwalker

noyade - an execution carried out by drowning

nugacity - triviality or frivolity

nympholepsy - passion or rapture aroused in men by beautiful young girls

obnubilate - to darken, dim, or obscure something (you make a better door than a window as my Nan would say)

ogdoad - a group or set of eight 

omophagy - the eating of raw food, especially meat

omphalos - the centre or hub of something

onolatry - the worship of donkeys or asses (we like big buts - shut up Brian!)

o-o - an endangered Hawaiian bird, a species of honeyeater (the larger birds look like this O-O, particularly when surprised by a honeyeater)

operose - involving or displaying a lot of effort

opsimath - a person who begins to learn or study late in life

orectic - having to do with desire or appetite

orrery - a clockwork model of the solar system, or the sun, earth, and moon

ortanique - a cross between an orange and a tangerine (also known as a fruit salad)

otalgia - earache

oxter - Scottish & N. English a person's armpit