The best replacement for instance is database.

The best alternatives to instance are rated as following:
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★★★★  static
★★★★  instant
★★★★  object
★★★  class
★★★  incidence
★★★  for example
★★  schema
★★  class variable
★★  static methods
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★  object java
★  type parameter revit
★  quest
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★  class methods
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★  for instances
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  default instance

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Speaking about instance, one probably shouldn't forget about key pair.

Other search terms related to instance and their ratings are:
★★★★★ key pair
★★★ singleton
connected rdbms instance
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instance
database
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