Butterflies veer crazily in opposite directions (6)
I believe the answer is:
nerves
'butterflies' is the definition.
(I've seen this in another clue)
'veer crazily in opposite directions' is the wordplay.
'crazily' indicates an anagram.
'in' means one lot of letters goes inside another.
'opposite directions' becomes 'ns' (abbreviations for north and south).
'veer' with letters rearranged gives 'erve'.
'erve' put within 'ns' is 'NERVES'.
(Other definitions for nerves that I've seen before include "Bodily fibres conveying sensations" , "They connect the brain with other parts of the body" , "Fibres that convey feelings" , "shows anxiety" , "Uneasy psychological state" .)