a household bowl for measuring dry grain: a Roman peck-measure holding about two gallons, big enough to be turned over a lamp
This word names a plain kitchen object: the standard bowl a household used to measure out grain, holding roughly two gallons (about 8.75 liters). The name came into Greek from the Latin word for the Roman peck-measure, part of a whole set of everyday commercial terms that spread with Roman rule. To people of the time it was as familiar as "bushel" once was to farmers, and it named both the fixed amount of grain and, as in the New Testament, the physical vessel that held it.
All three New Testament uses are the same picture, and the same object. Jesus says no one lights a lamp only to hide it under the measuring bowl instead of setting it on a stand where it can light the room. The saying leans on the fact that a peasant house had exactly one of each of these things, which is why each Gospel says "the" bowl, "the" lamp, "the" stand: the single measuring vessel every family owned was simply the nearest thing big enough to cover the flame. Luke tells the same saying a second time (Luke 8:16) using σκεῦος, the general word for any container, most likely so readers outside Palestine would picture the scene easily.
Scholars agree almost completely on what the word means and mostly on how the image works. The usual reading is plain common sense: a lamp exists to give light, so covering it defeats its whole purpose. A smaller group notes that people sometimes put a vessel over a lamp precisely to snuff it out, since blowing produced acrid smoke, so the picture may be not just of hiding the light but of killing it. Either way, the point rests on how ordinary the object is.