Learn English – Distinction between “pillage” and “plunder”

A couple of colleagues and I have been going through some Google NGrams. At first it seems quite conclusive that plundering is a far more sea worthy activity than pillaging, and plundering is certainly the more pirately thing to do:

In an actual example: British critic: and quarterly theological review, Volume 16 (pp. 516 to 518), they appear to use pillage and plunder interchangeably as nouns, but only plunder as a verb. This seems fitting for water-borne criminality.

In this discourse of plunder (page 2) pillage is said to be something that makes up plundering.

However, the further I read into the samples provided by the Google book search, it seems that pillage and plunder can be used interchangeably, it's just that plunder is a far more popular word.

In fact, although it is a much rarer occurrence than "pirates plundered", "pirates pillaged" does appear in literature. Some examples:

• The pirate's own book

• The history of the lives and action of the most famous highwaymen

• The pocket magazine

• Belgium historical and picturesque

Outside of buccaneering, there is a lot of synonymous usage of plunder and pillage - here are some examples:

In a text about the history of English government, on page 94 they write:

Commercial plunder, however, was to be more destructive than military pillage

On page 554 of The new encyclopædia; or, Universal dictionary of arts and sciences they define Pillage by using plunder. An later on page 687 they define plunder using pillage.

There seems to be no difference in the meaning of the two words in The works of the Right Honourable Edmund Burke, Volume 7 on pages 408 and 410

Again I find the same in "The Forum, Volume 17" (plunder, pillage)

So, in conclusion, it seems that plundering and pillaging are the same thing.