Sages develop substances with no definite boundaries (5)

I believe the answer is:

gases

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'substances with no definite boundaries' is the definition.
I can't judge whether this defines the answer.

'sages develop' is the wordplay.
'develop' indicates anagramming the letters.
'sages' anagrammed gives 'GASES'.

Can you help me to learn more?

(Other definitions for gases that I've seen before include "Compressible fluids" , "Eg, helium, nitrogen" , "Vapours" , "Hydrogen and carbon monoxide, say" , "rabbits" .)

I've seen this clue in The Irish Times.

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