bona vacantia en · NOUN
Etymology
Latin
Meanings
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(UK, uncountable) The principle that there is no unowned property, and that if there is no other owner then property vests in the Crown.
"The company asked also for an express vesting order concerning the land, which had legally gone to the Crown as bona vacantia" http://books.google.co.uk/books?id=WvY3AAAAIAAJ&pg=PA814&dq=bona+vacantia