Pronounced ab-ess-ed-air-ee-an, or ay-bee-ceed-air-ee-an, and meaning in alphabetic order. As in, ABCy. To be applied to alphabetically ordered bookshelves, to indices, or indeed to (the first six letters of) the word itself. Also can be spelt abecedarian (thanks to slow for pointing that out), if you feel so inclined (a spelling which is associated with the first pronunciation above). One of those words which can't possibly be a word, but is.