A tentacle is long, ropey thing that sticks out of an animal’s face. You probably think they’re gross. Octopuses probably think they’re cute.
You can use the word tentacle when referring to all kinds of things that grasp and hold, not just slithery creatures like octopi and jellyfish. But the word does have creepy associations, which is why “the tentacles of organized crime” is a more common expression than, say, the “tentacles of friendship.”