In 1864, Merriam published a greatly expanded edition, which was the first version to change Webster's text, largely overhauling his work yet retaining many of his definitions and the title, An American Dictionary.

The vocabulary was vastly expanded in Webster's New International editions published in 1909 and 1934, featuring over half a million words.

In 1961, Merriam overhauled the dictionary again, publishing Webster's Third New International, edited by Philip B. Gove, whose revisions sparked public controversy.

Many of the changes were in formatting, omitting needless punctuation, or avoiding complete sentences when a phrase was sufficient.

Others more controversial revisions signaled a shift from linguistic prescriptivism and towards describing American English as it was used at that time.

This dictionary is the preferred source "for general matters of spelling" by The Chicago Manual of Style, which is followed by many U.S.-based book publishers and magazines.

[6] The dictionary maintains an active social media presence, where it frequently posts dictionary-related content and its views on politics.

[7][8] In November 2021, for instance, Merriam Webster subtly accused Kyle Rittenhouse of fake crying at his trial in a tweet that went viral.

[9] In 1996, Merriam-Webster launched its first website, which provided free access to an online dictionary and thesaurus.

[11] The Merriam-Webster company once used a unique set of phonetic symbols in their dictionaries—intended to help people from different parts of the United States learn how to pronounce words the same way as others who spoke with the same accent or dialect did.

Hence, to enable computerized access to the pronunciation without having to rework all dictionaries to IPA notation, the online services of Merriam-Webster specify phonetics using a less-specific set of ASCII characters.

[5] Editors at Merriam spend about an hour a day looking at print sources, from books and newspapers to less formal publications, like advertisements and product packaging, to study the uses of individual words and choose things that should be preserved in the citation file.