Technical talk initially dismissed inert gas (5)
I believe the answer is:
argon
'inert gas' is the definition.
(I've seen this before)
'technical talk initially dismissed' is the wordplay.
'technical talk' becomes 'jargon'.
'initially dismissed' means to remove the first letter (the initial is dismissed).
'jargon' with its initial letter taken away is 'ARGON'.
(Other definitions for argon that I've seen before include "Noble gas, Ar" , "Inert gas, symbol Ar" , "Inert gas, present in small amounts in the air" , "elementary" , "17 [GAS]" .)