h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Other examples of words that are their own opposites are:
Chuffed (happy and sad)
scan (if you scan over a document with your eyes it's very brief, but if you do it with a computer it will go slowly and record all the detail)
Historicism (imitating history, or consciously avoiding historic techniques to produce something that will be associated with this point in history)
Leggings (baggy trousers worn over other trousers, or tight trousers you can wear under other trousers)

There are also pairs of words that sound like opposites but aren't:
vegetarian and humanitarian
income and outcome
unisex and bisexual
excite and incite
increment and excrement

Have to argue with the last one, as in the sentence

I got a small increment to my salary - it was a load of excrement!

Abbreviation must fit into this category as it is reallllllllllly long...

Note that "generally" is also its own opposite, see http://www.h2g2.com/F42754?thread=57902

Zaphod's comment reminded me of the heterological-autological paradox (This is more a logical oddity than a linguistic one, but bear with me)

Autological adjectives are adjectives that apply to themselves: ie pentasyllabic, humongous, mispeled, latinate, etc.

Heterological adjectives are adjectives that don't apply to themselves: ie big, monosyllabic, fictitious, etc.

The question is, to which of those two categories do the adjectives "heterological" and "autological" belong?

I suggest that 'autological' is an autological adjective, since this causes no logical inconsistency. However, the classification of 'heterological' is analogous to the Liar's Paradox: if it is heterological, it must be autological, and vice versa. So we need a new category: neuterological (or whatever). 'Neuterological' would, of course, be heterological.

~*~Amanda.

Actually, a better answer to the question of whether heterological is autological or heterological is mu. Mu is also the answer to the Zen koan, "what is the sound of one hand clapping?" It is meant to indicate an un-asking of the question, because the question itself is incoherent (though it may not seem to be). Another example is the town with one barber, in which everyone gets their hair cut and everyone in the town who doesn't get his or her hair cut by the barber cuts their own hair. So who cuts the barber's hair? The solution is that this is a faulty question; the situation simply cannot exist. That's what mu means. So basically, the question of whether heterological is autological or heteological depends on the incorrect assumption that all adjectives fit under one of the two categories. Trying to resolve the riddle by creating a new category, neuterological, is like trying to resolve the barber riddle by saying the barber is bald. It does resolve the dilemma, but misses the point of the question.

Cleave is a pretty good one. Two completely opposite definitions in the dictionary;

1. To bring together - cleavage

2. To split apart - cleaver

Another point to raise on this regards what it is that constitutes the properties of an adjective: for example, were you to write the word "green" in green ink, then it may be described as autological (or homological) whereas were you to write it in purple ink then it would be heterological.

The same could be said if one whispered "loud" or shouted, as often happens in classrooms, "quiet" (although usually as a command, rather than as an adjective.)

In either situation, the linguistic properties of the word depend entirely on the manner in which they are being used, rather than an inherent property that the word has.