a kiss: the act of pressing the lips to someone, a bodily gesture whose meaning depends entirely on the setting.
This is simply the ordinary word for a kiss. The Bible never treats a kiss as a single thing with one fixed meaning. The very same gesture could greet a guest, seal a reunion, show honor to a king, betray a friend, or pass between lovers. A kiss is a thing you do with your body to another person, and what it means is read off the situation, not off the word. So the seven places this noun appears in the New Testament cover a surprisingly wide range, from open devotion to outright treachery.
What makes the word memorable in the New Testament is not the gesture itself but who is being kissed. Five of its seven uses are commands to early Christians to greet one another with a kiss, calling it a holy kiss or a kiss of love. In the surrounding world a public kiss between people who were not family was unusual and could be scandalous, so the instruction was bold: it treated fellow believers, across differences of background, wealth, and gender, as if they were close kin. The two remaining uses, both in Luke, show the gesture at its tenderest and its ugliest: a kiss withheld from Jesus by a cool host, and a kiss used by Judas to hand Jesus over.
Because a kiss takes its meaning from context, the same warm act can be turned into its opposite. That is the point of the betrayal scene, where the customary sign of greeting and affection becomes the signal of arrest.