Rank,  【rampant】  mean growing or increasing at an immoderate rate.

Rank applies primarily to vegetation and implies vigorous, luxuriant, and often unchecked or excessive growth.

The term is common in metaphoric extension.

【Rampant】  is more widely applicable than rank; it implies rapid, often unrestrained or wild, spreading and is frequently applicable not only to what literally grows but to what extends or increases by contagion or diffusion.

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