It was originally published in Japan in 1942 as The Idiomatic and Syntactic Dictionary of English, written by A. Probably the best-known English monolingual dictionary for advanced learners is the Oxford Advanced Learner's Dictionary. Since the end of World War Two, the MLD has been a publishing phenomenon, with global sales running into tens of millions of copies, reflecting the boom in the English language teaching industry. The first English MLD, published in 1935, was the New Method English Dictionary by Michael West and James Endicott, a small dictionary using a restricted defining vocabulary of just 1490 words. But most of the activity in this field is in the area of dictionaries for people learning English. Monolingual learner's dictionaries have been produced for learners of several languages, including German, Spanish, Dutch, and Chinese.

And while the definitions in standard dictionaries are often written in difficult language, those in a monolingual learner’s dictionary aim to be simple and accessible. Dictionaries for learners include a great deal of information on grammar, usage, common errors, collocation, and pragmatics, which is largely missing from standard dictionaries because native speakers tend to know these aspects of language intuitively. MLDs are based on the premise that language-learners should progress from a bilingual dictionary to a monolingual one as they become more proficient in their target language, but that general-purpose dictionaries (aimed at native speakers) are inappropriate for their needs.

A Monolingual learner's dictionary (or MLD) is a type of dictionary designed to meet the reference needs of people learning a foreign language.

Meaning of monolingual