Answer:

theme

Answer	Crossword Clue
THEME	... park
THEME	Many a party has one
THEME	Principal melody

THEME	What many an amusement park has
THEME	It's developed in a sonata
THEME	A park may have one
THEME	English class assignment
THEME	Motif
THEME	This puzzle's is revealed at 61-Across
THEME	Writer's development
THEME	Composer's creation

THEME	School composition
THEME	Variation preceder
THEME	English assignment
THEME	Composer's base
THEME	A restaurant may have one
THEME	School assignment
THEME	Composer's basis
THEME	Basis of a musical composition

THEME	School essay
THEME	Unifying idea
THEME	Continuing thought
THEME	Kind of song or park
THEME	Kind of park