Start of a play

ACTONE

The first major division in Shakespeare’s Hamlet or any theatrical performance.

The clue "Start of a play" hints at the beginning section of a theatrical performance, which is called an "act." Instead of just "act," the answer is "ACTONE" because it combines "act" with "one" to literally mean the first act—like saying "Act 1" without the space. It’s a straightforward charade where the wordplay merges the two ideas into a single compact answer.