Saliva test involved with lip (7)
I believe the answer is:
spittle
'saliva' is the definition.
(I know that saliva can be written as spittle)
'test involved with lip' is the wordplay.
'involved with' indicates anagramming the letters (involved can mean confusing or complex).
'test' with its letters mixed up with 'lip' gives 'SPITTLE'.
(Other definitions for spittle that I've seen before include "Saliva ejected from mouth." , "39 [SPITTLE]" , "bodily fluid" .)