The phrase originates from the brutal military command to kill all enemy combatants on the battlefield rather than capture them, thereby eliminating future threats and avoiding the logistical burden of prisoners. By the mid-20th century, this literal instruction evolved into a metaphorical idiom describing a ruthless, uncompromising approach in any competitive arena, such as business, politics, or sports. The transition from a specific tactical order to a descriptor of relentless, merciless attitude encapsulates the conceptual shift from physical warfare to figurative conflict. Its grammatical conversion into a hyphenated compound adjective follows a common pattern in English for solidifying idiomatic expressions into modifiers.

This is a fixed adjectival phrase derived from a military idiom. It is not productively formed from separable modern English morphemes in the context of its current meaning.