Pierre or Marie
I believe the answer is:
curie
'pierre or marie' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for curie that I've seen before include "Marie ---, found radium" , "Pioneer in radioactivity" , "Nobel Prize winner for physics (1903) and chemistry (1911), d. 1934" , "Unit of radioactivity" , "Scientist" .)