Rearing (7)
'rearing' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for rampant that I've seen before include "Flourishing excessively as disease may be" , "Spreading unchecked" , "Growing or spreading uncontrollably" , "Mantrap (anag) - unrestrained" , "Unchecked - standing up on hind legs" .)
'rearing' is the definition.
('raise' can be a synonym of 'rear')
This is all the clue.
(Other definitions for raising that I've seen before include "Lifting" , "Growing" , "Bringing up" , "Promoting (in rank)" , "Elevating" .)