As I'm no doubt certain long-term readers of my various journals are well aware, I tend to be a bit fussy about word usage. I'm a big fan of the correct word in the correct place, as well as being somewhat intolerant (pronounced "shriekingly furious") about the wrong word being used in the wrong place. Mucking up "definite" and "defiant" because you pronounce "definite" with an "a" and therefore spell it the same way will certainly raise my blood pressure. Ditto using the words "taunt", "taut" and "taught" interchangeably (they aren't interchangeable - they're different words with different meanings). Don't
get me started about "lose" and "loose".
This is part of why I feel that a good sized dictionary (and by "good sized", I mean "hardcover, and heavy enough to kill small crawling things") is an essential part of any writer's toolkit.
No, MS Word Spell-check and Grammar check is not a good substitute. Here's why:( list below the fold )
A good dictionary will give you all the information you need about the words you're using in your fiction writing. It's worth investing in one, and using it as a backup to the spell-check program in your word processor of choice. Because here's another thing about dictionaries: they're generally created by a committee of people who are interested in words
and who have spent their lives being fascinated by words and the way words are used. Dictionaries are created by professional linguists, as opposed to the professional computer programmers and professional managers who create spell-check functions for word processors. I'm more inclined to trust a dictionary to be correct on matters of word choice and usage than a spell-check program - because a dictionary is more likely to have been edited by people who are interested in more than just the business end of town.
My personal preference is for the Concise Oxford Dictionary, because the bound copy I bought about five or so years back came with a version of the whole thing on disc, designed to be installed onto a computer. I use the PC version as a backup for the spell-check programs of whichever word processing package I'm using at the time - if the spell-checker picks something out as a possible misspelling, I'll check it against the dictionary. Most of the time, the difference is between UK and US English - I'll be spelling things with the extra "u" or similar, while the word processor tends to have problems with anyone not using US English like they say they're using in their computer settings (I use Commonwealth spellings and US keyboard settings because I'm from Australia - we use dollars and cents here as our default currency, and MS Windows doesn't come with a language setting for "English: Australian"). Rather than getting into a lengthy argument with my word processor, I just double-check things against the dictionary, and spend a certain amount of time telling spell-check that it's wrong.
 Oddly enough, there is an adjective meaning "made of or coloured silver" - it's "silvern". One for the poetically inclined in the FFVII fandom, and hopefully this will prevent me ever
having to see "silveret(te)" again.
ETA: edited to add cut 0730h GMT+8 26 JUN 2012