Not only are there many fascinating words there are also many fascinating types of words. One very interesting type is the Janus word. A Janus word is a word (such as cleave) having opposite or contradictory meanings. Janus words are also known as Two-Faced Words. The name comes from the Latin word Janus, the god who faces both ways.
Just a side thought - my high school yearbook was titled Janus. When I read the above definition I was intrigued. Our yearbook was named Janus to reflect looking both forward and back but, being a product of the 60's, we certainly could be called opposite or contradictory at times. :)
Some examples of Janus words -
To weather can mean "to endure" or "to erode."
Sanction can mean "to allow" or "to prohibit."
Fix can mean "a solution" (as in "find a quick fix") or "a problem" ("left us in a fix").
Clip can mean "to separate" (as in "clip the coupon from the paper") or "to join" (as in "clip the answer sheets together").
Left as a verb in the past tense means "to have gone"; as an adjective, it means "remaining."
Wear can mean "to last under use" or "to erode under use."
Buckle can mean "to fasten" or "to bend and then break."
The verb bolt can mean "to secure, lock" or "to start suddenly and run away."
Screen can mean "to conceal" or "to show."
To table a bill means in British English "to put a bill up for debate" but in American English "to remove a bill from debate."
Fast can mean "moving quickly" (as in "running fast") or "not moving" (as in "stuck fast").
"There are many such words, and they arise through various means. Called 'Janus words,' 'contranyms,' or 'auto-antonyms,' they include cleave ('to stick to' and 'to split apart') . . . and peruse and scan (each meaning both 'to read closely' and 'to glance at hastily; skim'). Usage writers often criticize such words as potentially confusing and usually single out one of the meanings as 'wrong,' the 'right' meaning being the older one, or the one closer to the word's etymological meaning, or the one more frequent when 18th-century grammarians began to examine language systematically."
(Jesse Sheidlower, "The Word We Love to Hate," Slate, Nov. 1, 2005)