bunny
Synonym discussion
Sense: noun/1
For this sense, 'rabbit' is the normal neutral word and works in everyday talk, school books, and science writing. 'Bunny' is softer and more affectionate, so adults often use it with children, pets, toys, or story characters. 'Bunny rabbit' is even more child-focused and can sound extra playful. 'Hare' is not just a style choice: it names a different animal with longer ears and legs, so it should not replace 'rabbit' or 'bunny'. Compare: 'The children fed a bunny at the farm' sounds warm and child-friendly, while 'The book explains how a rabbit lives' sounds neutral and factual.
Etymology
Bunny probably grew from bun, an older informal English word for a rabbit, with the ending -y, which often makes a word sound small or affectionate. It first named the animal itself and later spread to playful labels for certain kinds of people.