O que significa global corporate octopuses ?

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I highly suggest you understand what is metonymy so that you are able to figure out for yourself next time.

Metonymy is a figure of speech in which a thing or concept is referred to by the name of something closely associated with that thing or concept.

As such, by calling international businesses global corporate octopuses, the author is using metonymy.

How do we know that global corporate octopuses refer to international businesses? "global" means international, and "corporate" relates to companies. As such, when "global corporate" acts as an adjective that modifies the noun "octopuses", we know that the author is giving international businesses a nickname of "octopuses".

There is also another effect in referring to international businesses as octopuses. A trait of international businesses will be highlighted by a trait of octopuses. Usually, the author will explain immediately afterwards if it is not clear. However, if there is only one possible explanation, the author can choose to not explain and leave the reader to figure out for themselves. In this case, there can be multiple explanations but i can still give you one.

Similar to how octopuses are difficult to remove when they grab onto something, international businesses can be tough to uproot as they have much of the world in their grasp already.