Unit of pressure (6)
I believe the answer is:
pascal
'unit of pressure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pascal that I've seen before include "French mathematician, d. 1662 - SI unit of pressure" , "Seventeenth century French physicist" , "Unit of pressure, French philosopher and programming language" , "clever thinker" , "religious philosopher" .)