"Kindly," "passed,"and "house" are words that Dickinson uses in an unfamiliar or unexpected way in "Because I could not stop for Death."
Dickinson's depiction of death in the poem is unexpected. Her descriptions of it follow suit. The use of "kindly" is unexpected. One would not normally associate Death with politeness, but Dickinson's reflective capacity about death compels her to do so. The fact that Death is courteous and responds to the speaker in a "kindly" manner can be seen as unfamiliar. It is a different association than traditional expectations surrounding the purveyor of the ending of life.
The use of "passed" is another word employed in an unexpected manner. "Passed" and "death" usually reflect sadness and mourning, such as when someone has "passed on." The word indicates leaving others behind. However, when Dickinson uses it, "passed" indicates movement, progressing along a path. The speaker talks about how she and Death passed a school yard at recess, the "Fields" of grain, and "the Setting Sun" "passed" them: "Or rather – He passed Us –." In the use of "passed," Death and the speaker, with Immortality, travel together as companions: "We passed ...." They drove together in "the Carriage," with "Immortality" as a third companion, passing through life toward "Eternity": "the Horses' Heads Were toward Eternity –." There is no mourning, rather a contemplative mood struck.
Finally, "house" is used in a very unfamiliar manner. The idea of a "house" is accustomed to family life and the hearth. However, Dickinson uses it as a reference to a grave and coffin: "The Cornice – in the Ground –." This has become the "home" of the speaker, one where time has freely "passed": "Since then – 'tis Centuries –." This use of "house" reminds the reader that Death "kindly" waits for everyone. The term reflects a final destination. Given the traditional associations regarding death, using "house" to communicate such a reality is unexpected.