Administrator’s right of retainer

What does Administrator’s right of retainer mean in American Law?

The definition of Administrator’s right of retainer in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

In its earliest use the phrase referred to the right of the administrator of a decedent’s estate who was also a creditor thereof to “retain” from the estate the amount it owed him. It is now also used to cover the administrator’s right to deduct from the amount otherwise payable to a distributee of the estate the amount the distributee owes the estate. (There is also an essentially identical “executor’s right of retainer.”)