Part of a flight

STEP

Think of what you might climb to reach a higher level, especially in a series. It’s also a basic unit in a staircase or process.

"Part of a flight" is a clever play on words. While it could literally refer to a section of an airplane journey, here it hints at a "flight" as a series of stairs—like a flight of steps. The answer "STEP" fits because it’s a single part (or step) within that larger sequence. The clue works by using the less common meaning of "flight" to misdirect slightly before landing on the straightforward answer.