Definition of "Middlesex"

A former inland county of England, partly absorbed into the erstwhile County of London in 1889; finally abolished in 1965 and absorbed mainly into Greater London, the south-west corner of the county becoming Spelthorne Borough and included in Surrey.  examples

The central of the three historical counties of Jamaica, bordered by the counties of Cornwall in the west and Surrey in the east; named for the English county.  examples

Ellipsis of Middlesex County.  examples