Gas from lightweight individual (5)
I believe the answer is:
ozone
'gas' is the definition.
(I know that ozone is a type of gas)
'lightweight individual' is the wordplay.
'lightweight' becomes 'oz' (abbreviation for ounce, a light weight).
'individual' becomes 'one' (an individual is one person).
'oz'+'one'='OZONE'
'from' is the link.
(Other definitions for ozone that I've seen before include "Colourless gas soluble in alkalis and cold water" , "Colourless gas, O3" , "Gas in upper atmosphere" , "A gas; threatened layer in air" , "Clean, bracing air" .)