Angel Blade
A weapon capable of killing angels. It could be described as a long blade, or a short sword. It is referred to as the Sword Of Lucifer in the official episode summary released by The CW, although it is never referred to as this in canon. Angel killing blades are seemingly carried by all angels. This was shown to some extent when we see many angels carrying them on many occasions throughout Season 5.
Initially in Uriel's possession, Anna used it to kill him. It is possible Castiel obtained it when Anna was captured and taken prisoner by Heaven.
According to Uriel, only an Angel can kill another angel4.16 On The Head Of A Pin. But since Castiel gives his blade to the Winchesters to use on Anna5.13 The Song Remains The Same it could be surmised that this blade is usually only carried by angels, yet that doesn't mean it is not effective in the hands of a human.
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4.16 On The Head Of A Pin
Uriel, a supporter of Lucifer is trying to recruit angels to his cause, which is to help free Lucifer from hell. When they refuse Uriel kills them with the Sword of Lucifer. Eventually Anna uses it to kill him.
5.01 Sympathy For The Devil
As Zachariah tries to coerce Dean in agreeing to be the Archangel Michael's vessel, Castiel arrives, and attacks the angels with a blade which kills them. It appears to be the same blade used by Anna although this is unconfirmed.
5.13 The Song Remains The Same
Castiel carries the blade with him when he meets with Anna. It is also one of the items that Castiel puts in the bag he gives to Sam before they travel through time. A young Mary Winchester will then use this blade to defend herself against Anna, but it is knocked out of her hand.
5.18 Point Of No Return
Castiel uses the blade to kill two angels, each carrying an angel-killing blade of their own, before finding Adam Milligan in a grave. He later uses the blade to kill an angel who is guarding the Green Room before banishing himself and three other angels (all carrying their own angel-killing swords) with an Angel Banishing Sigil drawn on his chest.
