As mentioned in the above post, there is certainly at least a shade of irony in Dickinson's use of the word "kindly" in "Because I Could Not Stop for Death." The definition of irony, of course, is a contrast between two things; here the description of Death as a gentleman is a contrast to the stereotypical picture of Death as some kind of thief or villain. In any case, we don't generally expect Death to be kind.
On the other hand, "kindly" literally describes Death's actions in this poem. He drove the speaker of the poem slowly on this final journey. She is treated without "haste" and "with civility." Death takes her to her final resting place, and there is clearly no traumatic leave-taking involved. In fact, she says centuries have passed yet it feels like virtually no time at all has gone by.
Death was a gentleman who escorted her by carriage on the final journey of her life, and there is nothing negative about the experience. That means "kindly" can be taken literally as well as ironically.
I would say there is some irony in Death's "kindly" stopping, but the irony depends on one's perspective on death. Remember that irony is simply a juxtaposition of incongruous elements, putting two things together that do not belong together. In this poem, if the narrator does not want to die, then she cannot possible perceive Death to be kind as he stops for her. And there is certainly language to suggest that, since she says she "cannot stop for Death." Additionally, most of us, if we think of Death as a person, seldom think of him as a kind, courtly gentleman who will stop on the road to pick someone up as a favor. Having said that, I must also add that in some situations, we do see death as a kindness. When someone is suffering a great deal or is old and very tired, death can be a great kindness. So, you can see that the irony is a function of the perception of Death, an unkindness or a kindness.