Knowing the Roots
At least half of the words in the English language are derived from Greek and Latin roots. Knowing these roots helps us to grasp the meaning of words before we look them up in the dictionary. It also helps us to see how words are often arranged in families with similar characteristics.
For instance, we know that sophomores are students in their second year of college or high school. What does it mean, though, to be sophomoric? The "sopho" part of the word comes from the same Greek root that gives us philosophy, which we know means "love of knowledge." The "ic" ending is sometimes added to adjectival words in English, but the "more" part of the word comes from the same Greek root that gives us moron. Thus sophomores are people who think they know a lot but really don't know much about anything, and a sophomoric act is typical of a "wise fool," a "smart-ass"!
Let's explore further. Going back to philosophy, we know the "sophy" part is related to knowledge and the "phil" part is related to love (because we know that Philadelphia is the City of Brotherly Love and that a philodendron loves shady spots). What, then, is philanthropy? "Phil" is still love, and "anthropy" comes from the same Greek root that gives us anthropology, which is the study ("logy," we know, means study of any kind) of anthropos, humankind. So a philanthropist must be someone who loves humans and does something about it—like giving money to find a cure for cancer or to build a Writing Center for the local community college. (And an anthropoid, while we're at it, is an animal who walks like a human being.) Learning the roots of our language can even be fun!
Some common Greek and Latin roots:

Root (source) Meaning English words

aster, astr (G) star astronomy, astrology

audi (L) to hear audible, auditorium

bene (L) good, well benefit, benevolent

bio (G) life biology, autobiography

dic, dict (L) to speak dictionary, dictator

fer (L) to carry transfer, referral

fix (L) to fasten fix, suffix, affix

geo (G) earth geography, geology

graph (G) to write graphic, photography

jur, just (L) law jury, justice

log, logue (G) word, thought,
speech monolog(ue), astrology, biology, neologism

luc (L) light lucid, translucent

manu (L) hand manual, manuscript

meter, metr (G) measure metric, thermometer

op, oper (L) work operation, operator

path (G) feeling pathetic, sympathy, empathy

ped (G) child pediatrics, pedophile

phil (G) love philosophy, Anglophile

phys (G) body, nature physical, physics

scrib, script (L) to write scribble, manuscript

tele (G) far off telephone,television

ter, terr (L) earth territory, extraterrestrial

vac (L) empty vacant, vacuum, evacuate

verb (L) word verbal, verbose

vid, vis (L) to see video, vision, television

Authority for this chart: The Little, Brown Handbook by H. Ramsay Fowler and Jane E. Aaron, & Kay Limburg. 6th ed. HarperCollins: New York. 1995. By permission of Addison-Wesley Educational Publishers Inc.