The word pentacle originally meant 'any symbol that protects against evil spirits'. There are many of such symbols, only a few of which include a pentagram. During the modern age of Wicca, the word 'pentacle' acquired a second definition, due to sounding similar to the word 'pentagram', and the fact that wiccan pentacles use a pentagram.
The Pentagram is a reminder that all elements, directions and spirit are linked.