All 4 Uses

successor
in
Childhood's End
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Yet it was not, Stormgren knew, entirely consideration for his successor that made him anxious to see the end of this state of affairs.†
Chpt 3 *

successor = replacement
Yet that, he thought with a lifting of his spirits, was a problem for his successor.†
Chpt 4
There is no need for you or your successor to worry unduly about the Freedom League, even when it has recovered from its present despondency.†
Chpt 4
You have given birth to your successors, and it is your tragedy that you will never understand them-will never even be able to communicate with their minds.†
Chpt 20

successors = replacements

Definitions:

(1) (successor)
replacement -- typically a person who takes the job of another person, but it can also be a thing that replaces something else
(2) (meaning too rare to warrant focus)