Factoid on European country (5)
I believe the answer is:
state
'country' is the definition.
(synonyms)
'factoid on european' is the wordplay.
'factoid' becomes 'stat' (I've seen this in another clue).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'european' becomes 'E' (abbreviation e.g. EU).
'stat'+'e'='STATE'
(Other definitions for state that I've seen before include "eg Iowa" , "Condition of country." , "Condition; nation" , "eg Maine" , "Say; country" .)