Datum about European plane (5)
I believe the answer is:
facet
This might be a double definition.
'datum' is the first definition.
(thesaurus)
'european plane' is the second definition.
'facet' can be an answer for 'plane' (facet plane is a kind of plane). I am unsure of the 'european' bit.
'about' is the link.
Can you help me to learn more?
(Other definitions for facet that I've seen before include "Aspect - smooth cut surface" , "Side or surface, diamond or building" , "side of rock" , "Aspect or feature of something" , "(Gem) side; aspect" .)