Have you ever stopped to wonder why words mean what they mean--and when they came into use? Take this word for example:
Hostile (adj.). Late 15c., from Middle French hostile: "of or belonging to an enemy" (15c.) or directly from Latin hostilis: "of an enemy, belonging to or characteristic of the enemy; inimical," from hostis: "enemy" (see guest (n.)). The noun meaning "hostile person" is recorded from 1838, American English, a word from the Indian wars. Related: Hostilely.
Interesting? Only if you're fascinated by the development of the English language. The study of how words evolved--usually from foreign words, sometimes from slang--is called etymology. Look up a word in Webster's Dictionary and you'll likely get very little of a word's parental background. Look up that same word in an etymological dictionary, and you'll see it all, from earliest usage right up to the present.
This is important to you as a writer, of course, because your armaments are words. Use them correctly, and your writing becomes stronger. Use them incorrectly, and your writing becomes mush.
Etymological dictionaries make interesting reading for nearly everyone. But for a writer, they are mandatory: you know, sort of like Words 101. Best of all, you can find numerous etymological dictionaries free and online. [Online (adj.). In reference to computers, "directly connected to a peripheral device," 1950 (originally as on-line).] One that I use most often, both to pass the time of day and to sharpen my literary skills, is the Online Etymology Dictionary. Go ahead. Give it a shot and make my day!