Why is a matrix pencil called a pencil?

The Oxford English Dictionary has an example from 1665 of "pencil" in the sense of "A group of rays or a beam of radiation converging to or diverging from a point." And one from 1840 in the geometric sense of "A set of lines meeting in a point"

After Speaking about French, English, Italian and Russian I checked the Greek, my language. Then, I found the greek verb δέσμη which means "to bind".

My interpretation of the etymology is that pencil represents a group bound by a property. In the projective geometry (older in Greek) the term a pencil of lines, δέσμη ευθειών, means lines passing through a common point. It is like the common handle of the brush and the filaments - wire or bristles or other. It works with parallel lines also and then it can mean the light beam etc. Hesiod uses the verb as in "to tie together, as corn in the sheaf".http://www.perseus.tufts.edu/hopper/morph?l=de%2Fsmh&la=greek#lexicon . It is that old. Linearity follows the geometry notion e.g. of lines through a point.

The pencil, used for writing, in Greek as in Russian, is a different word and not a metaphore. I do not know why they coincide in English. Probably, because it means a paintbrush, but it is now obsolete.