Word that means intimidating
In general, Chaos is a malevolent spiritual force that represents the collective negative aspects of the psyches of every sentient being in the Milky Way Galaxy, and most likely in the wider universe.
Because Mankind is by far the most populous intelligent species in the galaxy of the late 41st Millennium, the Chaos Gods particularly embody Humanity's myriad and particular flaws as a people.
Just before the birth of the Emperor of Mankind on Terra in the 8th Millennium B.
C., three of the major Chaos Gods of the present, Khorne, Tzeentch, and Nurgle, had already begun to take form in the Warp, although it would take until the end of Terra's European Middle Ages midway through the 2nd Millennium (circa 1400 AD) for them to fully awaken.
Once the Necrons arose to challenge them and nearly wrought their extinction because of their alliance with the malevolent Star Gods known as the C'tan, the Old Ones created new psychic warrior races to battle the threat they posed, hoping that these species' stronger ties to the Warp and potent psychic powers would turn the tide against the Necrons and their C'tan masters in the ancient War in Heaven.
One of these races was the ancestors of the Eldar and among the others were the Krork, who may have been the ancestors of the green-skinned Orks.
Chaos, also known to its servants as the Primordial Truth or the Primordial Annihilator, and to the Imperium of Man as the Archenemy, is the universal and usually malign spiritual force embodied by the malevolent intelligent entities comprised of psychic energy that live in the Warp. The entities who embody Chaos are mostly daemons, but the term also encompasses those mortals who have thrown in their lot with Chaos, ranging from simple peasants and/or manufactorum labourers who serve as Chaos Cultists, to Traitor Imperial Guardsmen, planetary militia, Imperial nobles, Planetary Governors, and even the mighty Chaos Space Marines and Traitor Titan Legions of the Dark Mechanicus.
It is a great and raw force of change and power, and is both physically and spiritually corrupting, though it is not in itself necessarily "evil." While its adherents and servants act in ways that are often malevolent, some devotees of Chaos are more dedicated to the service of freedom and change than of the pure selfishness that Mankind and most other intelligent species define as nefarious.
This can also be invoked in works- especially those which are "family friendly" that wish to portray something in the story that could offend their target audience, so, in order to keep the show from being too salacious, if a scene is extremely disgusting or lewd, all we'll get is the characters describing it (or just their reactions) instead of actually seeing the scene play out.
Smells and tastes are a common form in visual media, as the audience has no other way to detect these aside from character reactions.
Chaos also offers those who serve it the opportunity to perhaps one day wield power and respect far beyond the dreams of most mortals' avarice.
For so many people, but particularly in the oppressive, feudal Imperium of Man, where too often family connections and inherited wealth are rewarded rather than ability, and where it is impossible on many worlds for a talented individual to ever better their lot, Chaos actually offers a substantial degree of freedom and the only real meritocracy that they have ever known.