The wiki page on dropIndex only mentions the syntax using a document for the index, as in

db.coll.dropIndex({x:1})

but an index can also be dropped by its name:

db.coll.dropIndex('x_1')

There is also a related bug SERVER-1887: If a custom name was specified during index creation, only the name syntax works and not the document syntax (except when using runCommand(

) directly). Maybe should be mentioned in a red warning box until the bugfix is released. See CS-4711 for more details about this issue.

The docs page on dropIndex is minimal and doesn't provide any examples.