Phurbu: Ritual Dagger

Tib., phur-bu, phur-pa
Skt., kila
dagger, nail, wedge

The terms phurbu and phurpa have different, yet very much related meanings:

Phurbu, first of all, signifies a three-sided ritual dagger sometimes made of meteorite-stone or otherwise from or iron or wood. Its handle usually depicts either the head of a triple-faced deity, a small sculptured skull, and sometimes also (part of) a dorje. With such a dorje/vajra, the Sanskrit name is vajrakila.
Phurbu also can refer to a deity personified as (or in) a ritual dagger.
Phurpa refers to a Tibetan Dagger Cult, the rituals of which have been preserved, taught and practiced by a selected number of monks within the Nyingma and Chöd traditions. In the latter school, a type of dagger is used with a handle that consists of a dorje mounted on a face mounted on a skull; it is known as rgyal-rigs mcod-phur. Even today, the present (14th) Dalai Lama is often accompanied by a trained and dedicated phurpa-monk as a body guard.

The most extensive information on the subject, albeit not always as complete or convincing as one would wish for, is to be found in a book by Marcotty; with bits and pieces appearing elsewhere in the literature on Tibetan schools and practices.

Marcotty, Thomas. Dagger Blessing: The Tibetan Phurpa Cult. Delhi: Mittal, 1987.