Pensieve

The Pensieve is an object used to review memories. It has the appearance of a shallow stone basin, into which are carved runes and strange symbols. It is filled with a silvery substance that appears to be a cloud-like liquid/gas; the collected memories of people who have siphoned their recollections into it. Memories can then be viewed from a non-participant, third-person point of view.

Pensieve seems to be a portmanteau, combining the words ‘pensive’ and ‘sieve.’ The latter is an object in which something may be sorted, drained or separated, and ‘Pensive’ is derived from French, and originally from the Latin ‘pensare,’ meaning ‘to ponder,’ and in common English usage means ‘thoughtful’ or ‘reflective;’ thus a ‘pensieve’ allows for the sorting of thoughts, or memories.

Harry entered the Pensieve again in 1998 with memories acquired from Severus Snape in his dying moments. Harry learned of Snape's friendship with, and unrequited love for, Harry's mother, Lily, the reason for Dumbledore's trust in Snape, and that Voldemort had inadvertently made Harry a Horcrux. Harry finally realises that Snape was on his side the whole time, starting from the time that Voldemort had threatened Lily. It was only that Snape could not stand to be around the child of his enemy, James Potter, whom Harry looks almost exactly like, and that Harry was living proof that Lily had loved another man. Apart from having hismother's eyes, Snape only saw James through Harry, even saying that he had his father's "knack for trouble". Harry used the Pensieve to collect information, the information was that Harry had to confront himself to death in order for Voldemort to die; since Harry himself was a Horcrux.