Are wood bows backed with synthetic materials considered a composite Bow..?  or sinew and raw hide per example.

Technically it would be considered a composite because you are combining 2 materials but bows backed with sinew, rawhide, wood or boo(other materials too) are considered backed bows. Asiatic style horn bows are considered composite bows with sinew back, horn belly and wood core.
BTW, sinew and rawhide are natural materials and not synthetic. FG is synthetic, ie. man made.

What Pat said.  A Self bow is made from a single stick of wood. 
Composite bows are made from several materials, natural or synthetic. 
A Tri-lam bow is a composite bow with three layers, each a different wood.
A modern fiberglass bow is a wood-fiberglass composite -- several thin wood strips sandwiched between strips of fiberglass.
A self bow backed with linen, rawhide, flax, sinew, is a composite bow.  BTW that backing in many cases is matched to another material on the belly of the bow, making for example a wood-horn-sinew composite

"A Tri-lam bow is a composite bow with three layers, each a different wood."   how could an all wood tri-lam be a composite when there are not 2 different materials.
Back to my original question  if synthetic material used on a wood bow ie.  as a backing considered a composite Bow.  Maybe I did not word the original question right.  Ooooopppppppss.   We actually got 1" of snow.   

A tri lam is a composite of different woods.  The belly/core/back all have different properties that together make up a composite wood bow.

Your example would be a composite.  For the same reasons mentioned above and because it's combining different materials.

Can I ask, why does it matter what you call it?

Can I ask, why does it matter what you call it?   No reason just curious.

Synthetic like fiberglass -- yes a bow backed with a synthetic is a composite bow.  A bow backed with fiberglass is a composite.  A bow backed with synthetic drywall tape is a composite bow.  A bow backed with a rayon polyester necktie, to prevent splinters rising, is a composite bow.

If it is NOT a single stick of wood or fiberglass, or metal -- it's a composite...

Well that hain't what I call them when lightning strikes them on the tiller tree:)