Rampant

[Sarah]

Rising with fore paws in the air as if attacking; -- said of abeast of prey, especially a lion. The right fore leg and right hindleg should be raised higher than the left. Rampant arch. (a) An archwhich has one abutment higher than the other. (b) Same as Rampantvault, below.-- Rampant gardant (Her.), rampant, but with the face turned to thefront.-- Rampant regardant, rampant, but looking backward.-- Rampant vault (Arch.), a continuous wagon vault, or cradle vault,whose two abutments are located on an inclined planed plane, such asthe vault supporting a stairway, or forming the ceiling of astairway.

[Sarah]

Occurring unchecked: Happening in an unrestrained manner, usually so as to be regarded as a menace
rampant inflation.

Botany growing wildly: Growing strongly and to a very large size, or spreading uncontrollably.

Fierce: Exhibiting ferocious behavior or fierceness of spirit.

Heraldry on hind legs: Describes a heraldic beast depicted rearing up, in profile, and with its forelegs raised, the right one above the left.

Construction with unequal supports: Having a support or an abutment that is higher on one side than the other.

[Sarah]

Cool / wicked / groovy / excellent / smart / fab / great / brilliant. Good, basically.

[Sarah]

Extending unchecked; unrestrained

[Jason Yan]

(of something bad) getting worse quickly and in an uncontrolled way:

[Donald Trump]

(especially of something unwelcome or unpleasant) flourishing or spreading unchecked.