Old woman ditches union leader, getting shot? (7)

I believe the answer is:

opaline

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

'old woman' is the definition.
'Opaline' can be an answer for 'woman'. I'm not certain of the 'old' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for opaline that I've seen before include "whitish glass" , "Translucent glass" , "Milk glass" , "Semi-translucent glass" , "Opaquish glass; iridescent" .)

I've seen this clue in The Times.

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