Bit of hip old city (5)

I believe the answer is:

ilium

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

This might be a double definition.

'bit of hip' is the first definition.
('ilium' is part of 'hip')

'old city' is the second definition.
'Ilium' can be an answer for 'city' (Ilium is an example). I am not certain of the 'old' bit.

Can you help me to learn more?

(Other definitions for ilium that I've seen before include "Large bone of the pelvis" , "Hipbone" , "Whence Aeneas fled" , "Large pelvic bone" , "classical city" .)

I've seen this clue in The Guardian.

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