Besides being slangy in appearance and sound, there is nothing remarkable about the word blog. It is short for Weblog and its etymon conveys what it is: a log (journal) on the Web that gives an account of a person's reflections and experiences. What might pique your interest is the histories of two relatively unfamiliar homographs of blog. They have absolutely no connection to the Internet blog—or to each other, for that matter—but the fact that blog was used many years prior to the Internet is surprising to many people.
Blog is entered in the 1898 volume of The English Dialect Dictionary as a figurative use of block and is said to be "used of anything resembling a block or log of wood." This sense, now obsolete, may be found at the end of the 19th century.
Meanwhile we have our eyes on a nice li’ll blog of a horse; when we have time we will hunt about for a market cart.
—Charles Lee, Paul Carah, Cornishman (in The Leisure Hour), Feb. 1898
There is also an older verb use of blog (defined by Wright as “to look sullen or sulky”), which dates back to the middle of the 18th century.
And thee be olweys wother agging or veaking, gawing or sherking, blazing or racing, kerping or speaking cutted, chittering or drowing vore o’ Spalls, purting or ghowering, yerring or chounting, taking owl o’ wone Theng or Pip o’ t’ather, chockling or pooching, ripping up or roundshaving wone t’ether, stivering or grizzeling, tacking or busking, aprill’d or a muggard, blogginf or glumping, rearing or snapping….
—Peter Lock, An exmoor scolding, 1750
Blog can also be found in Eric Partridge's A Dictionary of Slang and Unconventional English. It is defined as 19th-century schoolboy slang for "a servant-boy in one of the houses [on campus]" and is explained as a perversion of bloke. In the 20th century, this use of blog was extended to "a common boy of the town." There is also an entry for the verb blog used in 20th-century slang as a synonym of defeat.
These forms of blog gradually faded away, but by the end of the 20th century a new homograph became prevalent in the English language, the Web blog.