One possibly rearmed with fancy ideas (7)
I believe the answer is:
dreamer
'fancy ideas' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'one possibly rearmed' is the wordplay.
'one possibly' is an anagram indicator.
'rearmed' with letters rearranged gives 'DREAMER'.
'with' is the link.
Can you help me to learn more?
(Other definitions for dreamer that I've seen before include "Gerontius" , "He has visions" , "Romantic" , "Martin Luther King" , "description of an Oxford spire?" .)