Datum about European plane (5)
I believe the answer is:
facet
This clue 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'm not sure about 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" .)