Icebergs, ultimately, repeatedly melt (6)
I believe the answer is:
soften
'melt' is the definition.
(I've seen this in another clue)
'icebergs ultimately repeatedly' is the wordplay.
'ultimately' says to take the final letters.
'repeatedly' becomes 'often' (I've seen this before).
The last letter of 'icebergs' is 's'.
's'+'often'='SOFTEN'
(Other definitions for soften that I've seen before include "To moderate" , "Make more plastic" , "Mollify" , "Tenderise" , "Yield" .)