1) Bidirectional 2) Bifacial 3) Hand ax 4) Having two faces or fronts 1) Bidirectional 2) Bifacial 
Biface refers to a chipped stone tool which has been completely formed on both sides or faces. A biface knife, for instance, is completely chipped, flat, and often ovoid or bipointed in shape. The carefully chipped edges formed the working edge of the tool. An arrowhead or spear point is a specialized form of biface.
In reference to projectiles or tools, biface describes those examples which have been worked and exhibit flake scars along both faces or sides.
[adj] - having two faces or fronts
bifacial adjective having two faces or fronts; `the Roman Janus is bifacial`