Measure state period's tail unit (9)

I believe the answer is:

empennage

I'm a little stuck... Click here to teach me more about this clue!

'tail unit' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

'measure state period's' is the wordplay.
'measure' becomes 'em' (em is a kind of measure).
'state' becomes 'penn' (abbreviation for Pennsylvania).
'period' becomes 'age' (age is a kind of period).
'em'+'penn'+'age'='EMPENNAGE'

Can you help me to learn more?

(Another definition for empennage that I've seen is " rear section of plane".)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.