apposition
noun
ap·po·si·tion ˌa-pə-ˈzi-shən 
plural appositions
1
a
: a grammatical construction in which two or more usually adjacent words, phrases, or clauses (especially nouns or noun equivalents) that have the same referent stand in the same syntactical relation to the rest of a sentence (such as the poet and Burns in "a biography of the poet Burns")
b
: the relation between such words, phrases, or clauses
2
a
: an act or instance of apposing
specifically : the deposition of successive layers upon those already present (as in cell walls)
b
: the state of being apposed
appositional
ˌa-pə-ˈzish-nəl
adjective -ˈzi-shə-nᵊl
Example Sentences
In “my friend the doctor,” the word “doctor” is in apposition to “my friend.”
Recent Examples on the Web This type is called an apposition compound eye, meaning each lens acts independently to create a mosaic image of what a creature sees. 
Riley Black, Scientific American, 13 Aug. 2020 But other elements were recognizable, like the flat vowels and the plaid shirts and the helpful practicality, like the lonesomeness of the undifferentiated plains, like the apposition of wilderness and chain stores. Alexis Soloski, New York Times, 27 Nov. 2019
Riley Black, Scientific American, 13 Aug. 2020 But other elements were recognizable, like the flat vowels and the plaid shirts and the helpful practicality, like the lonesomeness of the undifferentiated plains, like the apposition of wilderness and chain stores. Alexis Soloski, New York Times, 27 Nov. 2019 Word History
Etymology
Middle English apposicioun, apposicion "addition, application, apposition in grammar," borrowed from Medieval Latin appositiōn-, appositiō "application, addition, syntactic juxtaposition," going back to Late Latin,"application, addition," going back to Latin, "comparison," from apposi-, variant stem of appōnere "to place near, put or fit on, contribute as an additional element" + -tiōn-, -tiō, suffix of verbal action — more at apposite
First Known Use
15th century, in the meaning defined at sense 1a
Kids Definition
apposition
noun
ap·po·si·tion ˌa-pə-ˈzi-shən
: a grammatical construction in which a noun is followed by another that explains it
In "my friend the doctor," the word "doctor" is in apposition with "friend."
Medical Definition
apposition
noun
ap·po·si·tion ˌap-ə-ˈzish-ən
1
: the placing of things in juxtaposition or proximity
specifically : deposition of successive layers upon those already present (as in cell walls) compare accretion, intussusception sense 2
2
: the state of being in juxtaposition or proximity (as in the drawing together of cut edges of tissue in healing)