Almost sit in gum (5)
I believe the answer is:
resin
'gum' is the definition.
(thesaurus)
'almost sit in' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'sit' becomes 'rest' (resting is a kind of sitting).
'rest' with its last letter removed is 'res'.
'res'+'in'='RESIN'
(Other definitions for resin that I've seen before include "Glue" , "plant extract" , "Sap product" , "Sticky material" , "Plant exudation" .)