Beginning to sniff instant glue (5)
I believe the answer is:
stick
'glue' is the definition.
(thesaurus)
'beginning to sniff instant' is the wordplay.
'beginning to' indicates taking the first letters.
'instant' becomes 'tick' (I've seen this before).
The first letter of 'sniff' is 's'.
's'+'tick'='STICK'
(Other definitions for stick that I've seen before include "Rod" , "Gear lever; adhere" , "Baton; gum" , "Endure" , "Staff - criticism" .)