Wiktionary
n. A non-serrated table knife with a dull edge and rounded point, designed for spreading butter on a piece of bread without tearing it.
WordNet
n. a small knife with a dull blade; for cutting or spreading butter
Wikipedia
In common usage, a butter knife may refer to any non-serrated table knife designed with a dull edge and rounded point; formal cutlery patterns make a distinction between such a place knife (or table knife) and a butter knife. In this usage, a butter knife (or master butter knife) is a sharp-pointed, dull-edged knife, often with a sabre shape, used only to serve out pats of butter from a central butter dish to individual diners' plates. Master butter knives are not used to spread the butter onto bread: this would contaminate the butter remaining in the butter dish when the next pat of butter was served. Rather, diners at the breakfast, the luncheon, and the informal dinner table use an individual butter knife to apply butter to their bread. Individual butter knives have a round point, so as not to tear the bread, and are sometimes termed butter spreaders. If no butter spreaders are provided, a dinner knife may be used as an alternative.
Colloquially, bread knives are sometimes referred to as butter knives, though technically incorrect.
Usage examples of "butter knife".
With her other hand, she reached for the butter knife, and with it began to score a deep pattern of marks on the coarse weave of the dark-blue table-cloth.
No one would have thought that red-haired Bridget Flaherty, who had a sun-defying white skin and a brogue that could be cut with a butter knife, had stolen her father’.
He wore a black suit, a few sizes too large, and a crooked bow tie, and if he had shaved, he had done so with a butter knife.
I don't know the difference between a fish knife and a butter knife.
My father paused with the tub of margarine in one hand and the butter knife in the other, and for an irrational moment I thought he might stab Grandma Mazur.
His own hands, very narrow and long-fingered, wielded the tiny silver butter knife as if he were dissecting a lizard in his workroom.
Without missing a beat, my mother took a butter knife out of the silverware drawer, scooped some icing off the top of the cake, smeared the icing on the side Bob had licked clean, and sprinkled coconut all around the cake.
I got up from the desk and went back to the kitchen, where I took out a butter knife and the jar of extra-crunchy Jif.