The word "since" is a conjunction used to indicate a time relationship between two events. It connects a past event to a present situation or another event, showing that one thing has been true or has happened from a specific point in time. For example, in the sentence "I have lived here since 2010," the word "since" links the year 2010 to the ongoing action of living in a place. Additionally, "since" can also express a cause-and-effect relationship. In this context, it explains why something is the case. For instance, in the sentence "Since it was raining, we stayed indoors," "since" indicates that the rain caused the decision to stay inside. This dual function makes "since" a versatile conjunction in English.