Below you will find guidance and examples of how to reference both a print dictionary/encyclopaedia and an online dictionary/encyclopaedia in the body of your work and in the reference list at the end.
American Psychological Association (2015) define...
...(American Psychological Association, 2015).
Merriam-Webster (n.d.) describe...
Group Author. (Year). Word defined. In Title (edition., page number). Publisher.
American Psychological Association. (2015). Mood induction. In APA dictionary of psychology (2nd ed., p. 667).
Group Author. (Year). Word defined. In Title. Publisher. Retrieved Month Day, Year, from URL
Merriam-Webster. (n.d.). Semantics. In Merriam-Webster.com dictionary. Retrieved January 4, 2020, from https://www.merriam-webster.com/dictionary/semantics
NB: Because entries in the Merriam-Webster's Dictionary are updated over time and not archived, include a retrieval date in the reference.
When the author and publisher are the same (as in the examples), omit the name of the publisher to avoid repetition.