Always poetically, that is strange (5)
I believe the answer is:
eerie
'strange' is the definition.
(eerie means odd or strange)
'always poetically that is' is the wordplay.
'always poetically' becomes 'eer' ('e'er' is an archaic version of 'ever').
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'eer'+'ie'='EERIE'
(Other definitions for eerie that I've seen before include "Sinister" , "Unnerving" , "Uncannily strange" , "Strangely frightening" , "Spooky, creepy" .)