The following APIs are available for commercial and non-commercial use in JSON format:
Merriam-Webster's Collegiate® Dictionary with Audio
Merriam-Webster's Collegiate® Thesaurus
Merriam-Webster's Spanish-English Dictionary with Audio
Merriam-Webster's Medical Dictionary with Audio
Merriam-Webster's Learner's Dictionary with Audio
Merriam-Webster's Elementary Dictionary with Audio (Grades 3-5)
Merriam-Webster's Intermediate Dictionary with Audio (Grades 6-8)
Merriam-Webster's Intermediate Thesaurus (Grades 6-8)
Merriam-Webster's School Dictionary with Audio (Grades 9-11)