True and false definitions, by Graham, Jo, Peter and Martin

This is a game we played, of making up imaginary definitions for unusual words. Of the five definitions of these words, four are false. can you guess the correct one? Answer will follow!

Mamelon
1. The supposed "missing link" between mammals and reptiles, hypothesized by Gaspar in 1893. It had both reptilian and mammalian features.
2. A rounded hill or protuberance
3. A piece of mediaeval armour, protecting the wrist of the lance-hand of a mounted knight.
4. A style of verse, popular in Renaissance France.
5. The small tendril growing from a guava

Nival
1. The smooth outer layer of suede after brushing. The suede is said to be "nival" after this
2. Growing in snow, like crocuses and snowdrops in a harsh winter
3. A mental state of extreme stress
4. A sail-maker's needle
5. A gymnastics move on the Rings, named after the gymnast from Belarus who first performed it

Patavinity
1. A weakness of the knees,leading to stumbling
2. A belief system found in parts of the Inca Empire in Peru, involving the worship of domestic pets
3. It comes from the Roman name for Padua, and means using words of Paduan dialect, as Livy tended to do: hence, provincialism in general.
4. A mental state of extreme stress
5. Being in a condition to experience visions