It’s actually quite up in the air, in regards to where the word nanny came from. The job role itself dates back several hundred years, with titles varying. It is often assumed that the name came from the vocabulary of children themselves, basically a name referring to “female adult other than mother”. In Greek, this term is nanna.
There is more recent research that shows that the word nanny is derived from the name Anne. This research suggests, that in Dutch, many who had the role of childcare in this capacity in the 1600’s were named Anne, called Nan or Nanny – and the name stuck to the job role. The modern definition, a person who provides child care, has been officially established since 1785.