Online encyclopedias, dictionaries, and thesauri can be difficult to cite as they are often updated. Use (n.d.) for no date, but add a retrieval date before the web address.
The following are patterns for how you might write a reference list entry for articles from a encyclopedia, dictionary, or thesauri.
Title of reference work. (n.d.). Title of entry. In Title of reference work. https://www.www.www
Encyclopædia Britannica. (n.d.). Progressive education. In Encyclopædia Britannica. Retrieved May 6, 2019, from https://www.britannica.com/topic/progressive-education
(American Psychological Association, 2020, pp. 324-235, 328)