Wolfram von Eschenbach's name for the Holy Grail. Oddly enough, his concept of the grail is not as a chalice or dish, as it is usually conceived, but as the stone from Lucifer's crown.
Technically, this word is nonsense--it looks like Latin, but it isn't. However, the words may actually be the following:
lapsit
- lapis: stone
- lapsus: fallen
exillis
- exilis: meager, poor
- exsilium: exile
- elixir: a potion
- ex illis: from them
Any of these meanings fits Wolfram's depiction of the Grail--a stone fallen from heaven that, when used, can work as an elixer of life. Moreover, the stone is from the crown of the exiled prince of angels, Satan, who is now in rather meager estates.
It could also refer to the Philosopher's Stone, or to the Kaba'a in Mecca.