A number made from three (5)
I believe the answer is:
ether
'a number' is the definition.
(I've seen this before)
'from three' is the wordplay.
'from' indicates an anagram (from the letters).
'three' anagrammed gives 'ETHER'.
'made' acts as a link.
(Other definitions for ether that I've seen before include "Rare atmosphere" , "Clear upper air" , "Some were put out by this" , "Gas - air - space" , "Former anaesthetic" .)