Venus was the Roman goddess of fertility and gardens, the equivalent of Aphrodite. Her name is traditionally derived from Latin venus, veneris, 'desire', 'grace', 'charm', 'sexual love', a word which is related to English 'venerate' and even 'winsome'. It also seems to link up with venia, 'grace or favour of the gods', and venenum 'magic drug', 'charm' (English 'venom').
As is to be expected, there have been a number of other attempts to explain the name, including vanus, 'empty' and venio, 'to come'. This latter interpretation was the one favoured by William Camden in his Remains Concerning Britain, although in citing it, he disapprovingly mentioned yet another etymology that had obviously been current: 'Coming to all, as Cicero derived it, à veniendo, a fit name for a good wench. But for shame it is turned of some to Venice.'
However, the name is actually almost certainly pre-Roman, as pointed out by Varro, the Roman scholar born in 116 BC, who wrote, cuius nomen ego antiquis litteris . . . nusquam invent, 'whose name I now found in previous writings'. The original Greek name of the planet Venus was either Hesperos ('evening'), Phosphoros ('light-bearing', see Phosphoros) or Eosphoros ('bearing the dawn', see Eos and Phosphoros).
More than one name was used of the planet since Venus can be observed in both the evening and the morning, and the Greeks thought that they were seeing two separate 'stars'. (It was Pythagoras, incidentally, who first suggested that it was actually a single heavenly body.) Of these three names, Hesperos, of course, was the planet's evening one, while Phosphoros and Eosphoros were alternative morning names.
Later, when the Greeks were eventually convinced that Venus was only a single planet, her name of Aphrodite appeared, this being recorded by Aristotle and his teacher Plato in the third century BC. Finally the Roman name came, although not before the Romans in turn had abandoned their own 'morning' and 'evening' names for the planet of Lucifer ('light-bringer') and Vesper ('evening', as English 'vespers'). (It was much later than this that Lucifer came to be a nickname of the Devil in Christian mythology.)