sea change 
noun
1A profound or notable transformation: recent years have witnessed a sea change in the fortunes of car safety as a marketable quantity...
- This marks a profound sea change for the Company, which is arguably the largest B-to-B publisher online.
- With every decision that marks a sea change on the telecom horizon, there's usually a technology solution to address it.
- Only a true partnership involving all stakeholders can make a real sea change.
Synonyms
transformation, change, alteration, modification, variation, conversion, revision, amendment, metamorphosis, transfiguration, evolution, mutation;
remodelling, reshaping, remoulding, redoing, reconstruction, rebuilding, recasting, reorganization, rearrangement, reordering, reshuffling, restyling, rejigging, reworking, renewal, renewing, revamping, renovation, overhaul, remaking;
revolutionizing, revolution, transmutation
humorous transmogrification
1.1Australian A significant change in lifestyle, especially a move from the city to a rural or seaside location: people are looking at sea changes for a better work-life balance...
- Ever since my family tasted the ultimate sea change three years ago my three girls are up at 4 every morning bar Sunday.
- Tasmania is consided by many to represent the perfect 'sea change' for those wishing to escape the concrete jungles of Melbourne or Sydney.
- It has been much discussed in the media with examples given of downshifting and sea changes.
Origin
From Shakespeare's Tempest (i. ii. 403).