Something beginning with cn...
Well, there's Cnut, of course, the guy who told the tide not to come in. Unfortunately King Cnut died in 1035, though, so he's no longer available for spotting.
(A quick word about the tide thing. There are three versions of the story: firstly, that Cnut had an insanely big head and thought he really could hold back the tide; secondly, that Cnut was trying to get his courtiers to be less fawning; and, thirdly, that he was trying to show that all power and splendour was rightly the King of Heaven's. The oldest story is the third one.)
Well, if we can't spot Cnut, then how about a cnidarian? That's a jellyfish, coral, hydra or sea anemone. They all have cnidocytes, too, which are things like tiny poison-bearing harpoons for killing their prey.
Easiest of all the cn words to spot is a cnemis, though, because most of us have two of them. Cnemis is the anatomical term for a shin or tibia, and has the rather lovely related adjective cnemial.
Look out for cnemial pads at any cricket match near you.
Spot the Frippet: something beginning with cn. Of these words, the C is, sadly, pronounced only in Cnut. Cnidarian is from the Greek knidē, meaning nettle, and cnemis is from the Greek knēmē, leg.