an arrow is or isn't a polygon?
An arrow can be a polygon. A polygon is any two dimensional plane figure. An arrow can, obviously, be a three dimensional object.
No. A polygon is a CLOSED figure.
A polygon is a shape that is closed with straight sides and the sides do not overlap like these. I don't know if an arrow is a polygon.
It could be, if it is a regular stick arrow then no.
An arrow head has 4 sides and it is a quadrilateral polygon
Yes, there is. For example, a box-letter arrow is a polygon. A stick-letter arrow is not, because it is not in 1 piece
It is an irregular polygon.
No but it is a quadrilateral because it has 4 sides
If it is the outline of an arrow, and is made up of only straight lines, then it is a polygon. I tried to "draw" one, as an example, but the browser used at this site completely messed it up.