Longman Dictionary of Contemporary English
Wiktionary
n. An electric accumulator battery driven vehicle, designed for the house to house delivery of fresh milk. Common in Europe, especially UK.
WordNet
n. a van (typically powered by electricty) with an open side that is used to deliver milk to houses
Wikipedia
In British English, a milk float is a vehicle specifically designed for the delivery of fresh milk. Today, milk floats are usually battery electric vehicles (BEV), but they were formerly horse-drawn. They were once common in many European countries, particularly the United Kingdom, and were operated by local dairies. However, in recent years, as the number of supermarkets, small independent grocers and petrol stations, and convenience stores stocking fresh milk has increased, many people have switched from regular home delivery to obtaining fresh milk from these other sources.