Column supporting Romania's borders is a two-edged sword (6)
I believe the answer is:
rapier
'two-edged sword' is the definition.
(I've seen this in another clue)
'column supporting romania's borders is a' is the wordplay.
'column' becomes 'ier' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'romania' becomes 'r' (abbreviation).
'borders' means to remove the middle letters.
'is a' becomes 'amp' (A is the symbol for the amp or ampere).
'amp' with its middle removed is 'ap'.
'r'+'ap'='rap'
'ier' after 'rap' is 'RAPIER'.
Can you help me to learn more?
(Other definitions for rapier that I've seen before include "Straight sword with narrow blade" , "A fencing sword for repair" , "Fine-bladed sword" , "fencing equipment" , "Long slender sword" .)