Revolutionary Ireland supports Spain -- that's weird (5)
I believe the answer is:
eerie
'weird' is the definition.
(both can mean strange or unsettling)
'revolutionary ireland supports spain' is the wordplay.
'revolutionary' says the letters should be written backwards (letters revolve around).
'ireland' becomes 'eire' (poetic name for Ireland).
'supports' is a charade indicator (letters next to each other) (bottom letters provide a support for the top ones).
'spain' becomes 'e' (abbreviation for Espana).
'eire'+'e'='eiree'
'eiree' in reverse letter order is 'EERIE'.
'that's' acts as a link.
(Other definitions for eerie that I've seen before include "Spooky, macabre" , "Spectral" , "Bloodcurdling" , "Mysterious" , "Ghostly" .)