The first documented appearance of the word "nerd" is as the name of a creature in Dr. Seuss's book If I Ran the Zoo (1950), in which the narrator Gerald McGrew claims that he would collect "a Nerkle, a Nerd, and a Seersucker too" for his imaginary zoo.

The slang meaning of the term dates back to 1951, when Newsweek magazine reported on its popular use in Detroit, Michigan. By the early 1960s, usage of the term had spread throughout the United States and even as far as Scotland.

Throughout this first decade, the definition—a dull person—remained constant and was, at the time, a synonym for "square" or "drip." It was only later, in the 1970s, that the word took on connotations of bookishness and social ineptitude.

An alternate spelling, as nurd, also began to appear in the mid-1960s or early 70s. Author Philip K. Dick claims to have coined this spelling in 1973, but its first recorded use appeared in a 1965 student publication at Rensselaer Polytechnic Institute.

Oral tradition there holds that the word is derived from "knurd" ("drunk" spelled backwards), which was used to describe people who studied rather than partied. On the other hand, the variant "gnurd" was in wide use at the Massachusetts Institute of Technology throughout the first half of the 1970s.

Other theories of the word's origin suggest that it may derive from Mortimer Snerd, Edgar Bergen's ventriloquist dummy, or the Northern Electric Research and Development labs in Ontario (now Nortel). The Online Etymology Dictionary speculates that the word is an alteration of the 1940s term nert (meaning "stupid or crazy person"), which is itself an alteration of "nut."

The term was popularised in the 1970s by its heavy use in the sitcom Happy Days.