Spot the Frippet: mortar.

 Apart from the word, what's the connection between this:  

photo by Evan-Amos

and this: 

Croatian Army mortar, photo by Ex13

and this?

photo by Pawal Wozniak

and this?

(and, yes, there actually is one).

Worked it out, yet?

Oh, all right, Here it is, then:

Spot the Frippet: mortar. This word comes from the Latin word mortārium, a basin in which mortar is mixed. The early forms of the weapon kind of mortar was not much more than a bowl with explosives inside it. 

Some mortar words come via the French word mortier, which is the stuff you mix in a mortārium.  

A mortar board, as in the academic hat, is so named because it looks like the small board used by bricklayers to hold mortar as they work. Plasterers use them, too.

photo by Arpingstone

By the way, in a metal-producing mine, a mortar is place where you crush ore, and this has given us a dialect (English Midlands) word mortar, meaning to trample.