Source : Webster's Revised Unabridged Dictionary (1913)

Backsaw \Back"saw`\ (b[a^]k"s[add]`), n. [2d back, n.+ saw.]
   A saw (as a tenon saw) whose blade is stiffened by an added
   metallic back.

Source : WordNet®

backsaw
     n : a handsaw stiffened by metal along upper edge