What is a “cranberry morpheme”?

The term “cranberry morpheme” is a linguistic term describing a particular kind of “bound morpheme”. A morpheme is the smallest meaningful unit in a language. “Free” morphemes can function independently as words (e.g. town, dog), but “bound” morphemes appear only as parts of words. For example, “un-“ appears only accompanied by other morphemes to form a word. Most bound morphemes in English are affixes, particularly prefixes (un-, il-, dis-) and suffixes, (-tion, -sion, -tive,-ation, -ible, and -ing).

Bound morphemes that are not affixed are called “cranberry morphemes”, a term coined by Leonard Bloomfield (April 1, 1887 – April 18, 1949). His influential textbook “Language”, published in 1933, presented a comprehensive description of American structural linguistics.

Cranberry morphemes are a special form of bound morpheme whose independent meaning has been displaced and serves only to distinguish one word from another, like in “cranberry”, in which the free morpheme “berry” is preceded by the bound morpheme “cran-“, meaning "crane" from the earlier name for the berry, "crane berry" and completely unrelated to the homonym “cran” with the meaning "a case of herrings".

Other cranberry morphemes in English include: “mit” in permit, commit, “ceive” in receive, perceive; “twi” in twilight; “cob” in cobweb (from the obsolete word “coppe” for a spider) and “-ing” in place names such as "Reading", "Dorking", "Washington", from an Old English term meaning "the people of".