Gas is initially escaping your tip within hearing (8)
I believe the answer is:
ethylene
'gas' is the definition.
(ethylene is a gas)
'initially escaping your tip within hearing' is the wordplay.
I cannot quite understand how this works, but
'your' could be 'thy' ('thy' historically meant 'your') and 'thy' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
(Other definitions for ethylene that I've seen before include "PVC component" , "It's found in coal gas, Tyne heel (anag.)" , "compound" , "Flammable hydrocarbon gas" , "natural gas product" .)