Some words tend to have straightforward definitions that are equally as straightforward when you consider the root words from which they sprang. Greek is rife with these kinds of words. Take one root, add a connecting "o" if you need to, add another root, add a suffix if you want, and voila! A new word. And use the meaning of the roots to come up with a good definition. A great example of this is the word heliotropism. This simply comes from two roots: helios, meaning "sun," and tropein, meaning "to turn." Then the noun ending -ism is appended. From here, it isn't hard to see that the word refers to plants that have a tendency to turn toward the sun. The sunflower is a great example of a plant that exhibits heliotropism.
Other words don't have such a direct relationship between their derivation and their definition. Take, for example, the word recalcitrant, which appears as a challenge word in the Latin section of Spell It. Recalcitrant means "obstinately defiant of authority or restraint." The word is also used to describe diseases that do not respond to otherwise effective treatment. Recalcitrant does come from the Latin root recalcitrare, meaning "to be stubbornly disobedient," but the root takes on a metaphorical meaning. The two key parts are the prefix re-, meaning "backward," and the root calx, meaning "heel." What does a heel have to do with being stubborn? Well, according to the Romans, a fair bit. You kick back at the authority figure who is asking you do to something you don't want to do...with your heel! (You can imagine stubborn young children doing this to their parents.) So from there, Romans took the two parts, put them together, and came up with the verb recalcitrare.
It's words like recalcitrant that can make etymology fun...and that can make definitions stick to the brain more effectively. See if other definitions you find have a similarly fun story behind them as you learn them.