Examine underground laboratory item (4,4)
I believe the answer is:
test tube
'laboratory item' is the definition.
(I've seen this before)
'examine underground' is the wordplay.
'examine' becomes 'test' (testing is a kind of examining).
'underground' becomes 'tube' (the London Underground is nicknamed the Tube).
'test'+'tube'='TEST-TUBE'
(Other definitions for test tube that I've seen before include "item of scientific use?" , "Scientist's cylindrical glass" , "used by chemist" , "Chemistry lab item" , "Hollow cylinder for the laboratory" .)