Hi Raghavi,

Let's consider the term "behavior" as an example. If you search "behavior" in Merriam-Webster's dictionary, which is a US English dictionary, you will get a page that provides the definition of behavior, synonyms, etc. However, if you search "behaviour" in the same dictionary, you will get a result which says "behaviour" is a chiefly British variant of "behavior". 

Though "behaviour" is present in Merriam-Webster's dictionary, it is not a primary entry. It is the variant of the primary entry "behavior". 

Can you please try searching any US word in Lexico dictionary and let us know what you find?