Technical talk is initially just gas (6)
I believe the answer is:
jargon
'technical talk' is the definition.
'initially just gas' is the wordplay.
'initially' says to take the initial letters.
'gas' becomes 'argon' (I've seen this before).
The initial letter of 'just' is 'j'.
'j'+'argon'='JARGON'
'is' acts as a link.
(Other definitions for jargon that I've seen before include "Specialised terminology" , "Professional terminology" , "Technical language" , "Language specific to an activity" , "Specialist language" .)