"Killer" and "Knock-out"
Although "knock-out" can mean a blow to an opponent that renders them unconscious, and "killer" may refer to a person, animal, or thing that kills, in this context, those two words are synonymous to beautiful, pretty and gorgeous.
"Knockout" is a very beautiful, attractive, or seductive looking woman. You can think of it figuratively like her looks were so stunning that they "knocked you out".
"Killer", on the other hand is connected to the word "dead", which is a slang term for the word very, as in she is very beautiful. “She’s undeniably gorgeous” plays on the idiom drop dead gorgeous. It's someone so beautiful you are too stunned to move or look away.
Speaking of beautiful, Kim Kardashian goes to work looking stunningly gorgeous! The reality star posted a picture on Instagram showing off her newest photo shoot look. Read more at Hollywood Life.