Visionaries (5)
'visionaries' is the definition.
(dreamer is a kind of visionary)
This is all the clue.
(Other definitions for dreamers that I've seen before include "They conjure up nocturnal fantasies or impractical ambitions" , "Impractical people who live in the mind" , "Dames err about fantasists" , "Idealists or wishful thinkers" .)
'visionaries' is the definition.
('seer' can be a synonym of 'visionary')
This is all the clue.
(Other definitions for seers that I've seen before include "Prophets" , "They have visions of the future" , "wise men" , "They divine the future" , "Visionaries" .)