Prudence and Regina getting off freight train (6)

I believe the answer is:

thrift

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'prudence' is the definition.
(thrift is a kind of prudence)

I can't explain the rest of the clue.

(Other definitions for thrift that I've seen before include "Maritime growth" , "Practise this to save money" , "Careful use of resources" , "Careful control of resources" , "Careful spending" .)

I've seen this clue in the Irish Times.

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