demarcation:  As its form and meaning would suggest, demarcation is indeed related to mark, but only in a distinctly roundabout way. The word comes, possibly via French, from Spanish demarcación, a derivative of the verb demarcar ‘mark out the boundaries of’, which in turn is descended ultimately from the same prehistoric Germanic ancestor as English mark ‘sign, trace’.
It originally came into English in very specific application to the boundary line between the Spanish and Portuguese spheres of influence in the New World, as laid down by Pope Alexander VI in a bull of 4 May 1493. In Spanish this was the linea de demarcación (in Portuguese, linha de demarcação). By the middle of the 18th century the word was being used in English in much more general contexts.
The familiar modern phrase demarcation dispute, relating to inter-union squabbles, dates from the 1930s.
c. 1752, from Spanish linea de demarcacion or Portuguese linha de demarcaçao, name of the line laid down by Pope Alexander VI, May 4, 1493, dividing the New World between Spain and Portugal on a line 100 leagues west of the Cape Verde Islands. Applied from 1801 to other lines dividing regions. From Spanish de- (see de-) + marcar "to mark the boundaries of," from a Germanic source (see mark (n.1)).
1. It was hard to draw clear lines of demarcation between work and leisure.
2. Talks were continuing about the demarcation of the border between the two countries.
3. There is no sharp demarcation between these two types.
4. A sharp demarcation of adventive embryos from zygotic embryos cannot be drawn.