n. The act of joining; the state of being joined. The thing joined.n. In civil law, the joining of one person's property to that of another permanently, as the building of a house upon another's land, painting of a picture on another's canvas, and the like.n. In mathematics, the process of obtaining the domain Ω from the domain Ω by adding to it the number a which does not already belong to it, and adding also all numbers arising from a finite number of additions, subtractions, multiplications, and divisions involving a and all numbers in the domain Ω. See the extract.