Element in technical speech Jack ignored (5)
I believe the answer is:
argon
'element' is the definition.
(argon is a chemical element)
'technical speech jack ignored' is the wordplay.
'technical speech' becomes 'jargon'.
'jack' becomes 'J' (playing card abbreviation).
'ignored' is a deletion indicator.
'jargon' with 'j' removed is 'ARGON'.
'in' is the link.
(Other definitions for argon that I've seen before include "Inert gas used in light bulbs" , "Noble gas, atomic number 18" , "Inert gas, present in small amounts in the air" , "noble element" , "Inert eighteen ac gas" .)