the quality of being similar
"The striking similarity between the two paintings suggests they might have been created by the same artist."
a Gestalt principle of organization holding that (other things being equal) parts of a stimulus field that are similar to each other tend to be perceived as belonging together as a unit
"The audience instinctively grouped the identical blue dots into a single shape, illustrating the similarity principle where like elements are perceived as part of the same whole."
Closeness of appearance to something else.
"The twin brothers had a striking similarity in their facial features, making them nearly impossible to tell apart at first glance."
In plain English: Similarity is when two things share some of the same features or qualities.
"The striking similarity between the two paintings made viewers wonder if they were by the same artist."
Usage: The correct spelling is similarity, though many people mistakenly write it as similarly or confuse it with the adjective similar. Use this noun when referring directly to the quality of two things looking alike, rather than using an adverb like similarly to describe how something happens.
This word comes from the French term similarité, which combines the root meaning "alike" with a suffix indicating a state or condition. Essentially, it describes the quality of being similar to something else.