What's a Cubit?

There is a footnote in my Bible (Judges 3:16) that says that this dagger was actually a foot long, but this story is much more impressive if the dagger was actually a 2 edged sword...is the “cubit” in verse 16 a traditional cubit or just one foot?

16 But Ehud made him a dagger which had two edges, of a cubit length; and he did gird it under his raiment upon his right thigh.
17 And he brought the present unto Eglon king of Moab: and Eglon was a very fat man.
18 And when he had made an end to offer the present, he sent away the people that bare the present.
19 But he himself turned again from the quarries that were by Gilgal, and said, I have a secret errand unto thee, O king: who said, Keep silence. And all that stood by him went out from him.
20 And Ehud came unto him; and he was sitting in a summer parlour, which he had for himself alone. And Ehud said, I have a message from God unto thee. And he arose out of his seat.
21 And Ehud put forth his left hand, and took the dagger from his right thigh, and thrust it into his belly:
22 And the haft also went in after the blade; and the fat closed upon the blade, so that he could not draw the dagger out of his belly; and the dirt came out.
23 Then Ehud went forth through the porch, and shut the doors of the parlour upon him, and locked them.
24 When he was gone out, his servants came; and when they saw that, behold, the doors of the parlour were locked, they said, Surely he covereth his feet in his summer chamber.
25 And they tarried till they were ashamed: and, behold, he opened not the doors of the parlour; therefore they took a key, and opened them: and, behold, their lord was fallen down dead on the earth.
26 And Ehud escaped while they tarried, and passed beyond the quarries, and escaped unto Seirath.
27 And it came to pass, when he was come, that he blew a trumpet in the mountain of Ephraim, and the children of Israel went down with him from the mount, and he before them.
28 And he said unto them, Follow after me: for the LORD hath delivered your enemies the Moabites into your hand. And they went down after him, and took the fords of Jordan toward Moab, and suffered not a man to pass over.
29 And they slew of Moab at that time about ten thousand men, all lusty, and all men of valour; and there escaped not a man.
30 So Moab was subdued that day under the hand of Israel. And the land had rest fourscore years.
Judges 3

 

What? No Bill Cosby jokes?

didn't he do a routine (a long time ago...)about noah....after getting the instructions to build the ark, noah asked God: what's a cubit?

 

[at the risk of hijacking my own thread] i looked it up on the internet. it's from 1963...now, i feel old(!) did you know that it has been digitally remastered and available for downloading ? i listened to a couple clips...and heard How long can you tread water? a couple times...