Quantity helping to raise fertility (5)

I believe the answer is:

litre

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

'quantity' is the definition.
(litre is a kind of quantity)

'helping to raise fertility' is the wordplay.
'LITRE' is hidden back-to-front in amongst the letters.
But, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for litre that I've seen before include "One thousand cubic centimetres" , "quantity of drink" , "Unit of liquid measure" , "Metric unit of volume" , "One cubic decimetre" .)

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