Occasions for millions breaking links (5)
I believe the answer is:
times
'occasions' is the definition.
(I've seen this before)
'millions breaking links' is the wordplay.
'millions' becomes 'm' (abbreviation).
'breaking' means one lot of letters goes inside another.
'links' becomes 'ties' (tying is a kind of linking**).
'm' going inside 'ties' is 'TIMES'.
'for' is the link.
(Other definitions for times that I've seen before include "''For the ..., they are a'changin'''(Bob Dylan)" , "Paper" , "See 1" , "Big Apple's theatre district" , "measures the length of something" .)