According to David R. Wilton, management consultant and amateur etymologist, the origin and evolution of the word computer is rather straightforward.
Computer derives directly from the Latin computus and computare .
Putare means to reckon, and com is an intensifying prefix. The use of computer to refer to a person who does mathematical calculations dates to at least 1646. The verb form to compute dates from about the same time, with the first recorded usage in 1631. The earliest reference in the OED2 to electronic computer is in 1946. However, from the context of the citation, it is obvious that the term was in use prior to 1946.