Cliff externally eroded with swell rising (4-3)
I believe the answer is:
lift-off
'rising' is the definition.
(rising up)
'cliff externally eroded with swell' is the wordplay.
'externally eroded' means to look at the middle letters (the external edges of the word are removed).
'with' is a charade indicator (letters next to each other).
'swell' becomes 'toff' (wealthy or high-class person).
The middle letters of 'cliff' are 'lif'.
'lif'+'toff'='LIFT-OFF'
(Other definitions for lift-off that I've seen before include "Start of rocket's journey" , "Moment of rocket's launch" , "Launch (of rocket)" , "Instant when rocket leaves launching pad" .)