1. Floccinaucinihilipilification - "the act or habit of estimating or describing something as worthless, or making something to be worthless by deprecation".
With 29 letters, it is the longest non-technical word in the first edition of the Oxford English Dictionary (OED), which presents it as "enumerated in a well-known rule from the Eton Latin Grammar". The OED dates its first use in literature at 1741 in William Shenstone's Works in Prose and Verse: "I loved him for nothing so much as his flocci-nauci-nihili-pili-fication of money".
2. Mesonoxian - of or related to midnight.
3. Tyrotoxism - poisoning by cheese or any milk product.
4. Zabernism – an obsolete word meaning 'the abuse of military power or authority; unjustified aggression'. From the name Zabern, the German name for Saverne in Alsace, where in 1912 an overeager German subaltern killed a cobbler who smiled at him.
5. Rastaquouere - a social climber.
6. Finnimbrun - obs. rare a trifle, a gimcrack.
7. Lamprophony – loudness and clarity of voice.
8. Mungo - adumpster diver, one who extracts valuable things from trash.
9. Erinaceous - of the Hedgehog family; like, or characteristic of, a hedgehog.
10. Selcouth - unfamiliar, rare, strange, marvelous, wonderful. For example: The List Universe is such a selcouth website!