There is no canonical answer for which word are the various Power Words. See this D&D 5e reddit post regarding some tables' choices. Yes, I know we're talking about Pathfinder, but the Power Words go back to PF1e's source material... even so far back as the first Greyhawk supplement in 1975. Greyhawk, if you haven't heard the name, is the setting used by Gygax in the original iterations of D&D when he was modifying it from Chainmail. I know of no source, from Greyhawk or more recent, for D&D or Pathfinder, that defines the Power Words.
Regardless of what the word is, it cannot simply be hidden in speech. All spellcasting, even if it is only verbal (or even no components via metamagic), is obvious in the Pathfinder rules barring the use of special abilities such as conceal spell.
From the FAQ:
Although this isn’t directly stated in the Core Rulebook, many elements of the game system work assuming that all spells have their own manifestations, regardless of whether or not they also produce an obvious visual effect, like fireball. You can see some examples to give you ideas of how to describe a spell’s manifestation in various pieces of art from Pathfinder products, but ultimately, the choice is up to your group, or perhaps even to the aesthetics of an individual spellcaster, to decide the exact details. Whatever the case, these manifestations are obviously magic of some kind, even to the uninitiated; this prevents spellcasters that use spell-like abilities, psychic magic, and the like from running completely amok against non-spellcasters in a non-combat situation. Special abilities exist (and more are likely to appear in Ultimate Intrigue) that specifically facilitate a spellcaster using chicanery to misdirect people from those manifestations and allow them to go unnoticed, but they will always provide an onlooker some sort of chance to detect the ruse.