Degeneration

Description
Degeneration is the process of a word's meaning turning more negative as time passes; degeneration can also be called pejoration.

Examples
Silly : In old English silly meant "blessed", it became to mean "foolish" since people who are blessed are often innocent and guileless, therefore, the connotation evolved to "innocent". The word finally metamorphed to "foolish" because innocent people are innocent because they are too dumb to be anything else and the wise people of the world decided to take advantage of that.

Awful: Back at the 1600s the word amful meant "awe-inspiring". Now, the connotation the OED gives is "causing dread; terrible, dreadful, appalling."

Artificial: the word artificial meant "of artistic value" during the 1600s, now artificial is defined by the OED as "Opposed to natural. Of a thing: made or constructed by human skill, esp. in imitation of, or as a substitute for, something which is made or occurs naturally; man-made."

Amusing: the connotation for amusing from the 1600s is "riveting", currently it is defioned by the OED as "beguiling or cheating".

Villan: When the word villan first came to be, it meant "farm laborer or related to a villa or country estate". The word eventually changed it's meaning to "one who has all the bad qualities which in an aristrocraticage the gentry attributed to the lower classes."

Verbose: literally means "full of words", now is defined as "a tiresome excess of language"