open compound noun

An open compound noun is a compound noun that is written with spaces between its word components. This is in contrast to closed compound nouns, which are written as a single word, or hyphenated compound nouns, which use hyphens to connect words.123

Examples of open compound nouns include "high school," "ice cream," and "post office". The spelling of compound words can sometimes be inconsistent, but generally, when a noun + noun compound is short and established, it is often written as an open compound. Other types of compounds, such as adjective + noun compounds, are also frequently written open, like "genetic code".24