ponardo

No -ard- suffix. Esperanto has none, and it never has: the -ard you can see here is French, and it came in fused. Ponard- is one root. The temptation is stronger than usual because a handful of borrowed words share the ending - bastardo, standardo, bulvardo - and a run of three or four words with the same tail is exactly the pattern the affix system trains you to notice. Here the pattern is a coincidence of French morphology, not a piece of Esperanto, so there is nothing to decompose.

What separates it from the other blades. Glavo is a sword: long, two hands or one, carried openly. A ponardo is short, straight and pointed, made for stabbing rather than cutting, and its defining feature in every language that has a word for it is that it can be hidden. Tranĉilo is the ordinary knife you eat with, and ponardego is the oversized one, roughly what a Roman pugio was. The verb ponardi exists and means to stab with one.

Where you meet it. Almost entirely in historical and literary Esperanto: translations of Shakespeare, of the classics, of anything with a conspiracy in it. In the modern world a ponardo is a museum object, which is the right way to hold the word. Note the family beside it - pugno for fist is unrelated in Esperanto even though the French ancestor came from exactly that, because Esperanto took pugno straight from Latin pugnus and ponardo from French, so the two arrived by different doors from the same house.