A single-edged knife, about the size of a typical kitchen butcher knife but with an absolutely straight back and cutting edge. so the blade is shaped like a long narrow right-angle triangle. Unfortunately a search for “triangular” knives gives results for triangular-cross section (i.e., three-edged) knives.
Sounds like a type of butcher’s knife. Or maybe a Japanese boning knife.
If it looks like this it’s a deba
Can you post a picture? Use Photo bucket or similar and post the image link.
My immediate thought is keyhole saw but most people wouldn’t call this a knife. Too toothy.
Is this a kitchen tool or something from the workshop?
Err… duh. I thought I’d found it in a box in the basement, but it turned out to be another old knife I’d put away. I used to have one like I described, but it must have gotten tossed.
The deba is close but the spine and edge met at a point with no tip work.
Mostly they have a slight bevel on the spine near the tip, but ones with a straight spine are common enough.