An undergarment of buttfloss underwear that also has one or more chains for erotic effect. These nasty little things are hard to come across, but usually the most random of people have one.
The other night I snuck into Jessica's house and found a chainish thong in her closet!
In reference to the saying "off the chain.", Chainless is above and beyond even ever having a chain to be broken away from. To refer to something as being "Chainless" you are making someone, or thing to be close, or to be the best; in terms of fun, exciting, outlandish, or crazy. All of which are in a good way.
1. Yo Sean's party last night was chainless.
2. Did you see that outfit she was wearing? That shit was chainless.
3. Sean is just straight chainless.