Catchy
Part of speech: adjective
Definition: Instantly appealing and memorable (of a tune or phrase).
Example sentence: We're not just going to take some songs from a focus group in Nashville where people are sitting around in a circle having appointments trying to write catchy songs so they can sell them to a band like us.
Difficult
Part of speech: adjective
Definition: hard, not easy, requiring much effort
Example sentence: There is nothing more difficult to take in hand, more perilous to conduct, or more uncertain in its success, than to take the lead in the introduction of a new order of things.