Illuminating talk? (3)
I believe the answer is:
gas
'talk?' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for gas that I've seen before include "Nitrogen, say" , "Something exciting" , "It may be natural" , "Something delightful" , "Form of fossil fuel" .)