Were you looking for the Web of Ungoliant?
The Mystery web is a semi-rare drop of the Mirkwood Spider that is said to contain the remains of its last meal.
Once thrown by right-clicking, it will drop various items (some useful, some not so much) including, but not limited to: leather armour, bones, swords, rings, gold nuggets, silver nuggets, very rarely mithril nuggets, iron, rotten flesh, compasses, weapons and daggers, or even a slice of melon (this is one of two ways to obtain melons in Middle Earth, the other being a semi-rare spawn in Far Harad).
However, the player should never think that a mystery web marks the end of their fight, because the Mystery Web can also spawn small Mirkwood Spiders (any type of them can spawn).
Although this item is technically a "weapon", owing to the fact that it can be thrown, it deals neither damage nor knockback to its target.
All these rates are based off throwing around 209 mystery webs in-game. Drop rates for all pieces of armour are the same, and one random piece from the set is chosen when the web is thrown.
Due to the sample size, rarities for the most rare items (i.e. mithril nuggests) may not be entirely accurate.