Experiment by friend, insignificant (6)
I believe the answer is:
paltry
'insignificant' is the definition.
(thesaurus)
'experiment by friend' is the wordplay.
'experiment' becomes 'try' (I've seen this in other clues).
'by' means one lot of letters go next to another.
'friend' becomes 'pal' (pal is a kind of friend).
'try' after 'pal' is 'PALTRY'.
(Other definitions for paltry that I've seen before include "Feeble" , "Petty - base" , "not worth considering" , "Insignificant, trifling" , "Trival, Inconsequential" .)