When designing something new, nothing seems to matter more than getting the terminology right. If you don't name things precisely—one concept, one word—you're likely to confuse yourself. And if you don't name them concisely, people won't bother to use your terms, and they'll confuse themselves when they try to talk about what you've built.
The API designer's most important tool is the thesaurus. Which, contrary to what you might think, does not come from the Greek words for “god lizard”, but from the word for “treasure”.