終わる

「終わる」expresses the idea of completing, finishing an action. It is not used to describe natural phenomena or bodily conditions.
The difference between 「終わる」and 「切る」is that 「終わる」emphasizes the "ending of the action," while 「切る」 emphasizes "accomplishing the goal of the action." For example, "書き終わる" simply means "to finish writing," without specifying whether the work has been completed or not. "書き切る," on the other hand, implies "finishing writing" but also implies that the work has been completed, or at least the writer has achieved their intended goal.