One that speaks two languages – is bilingual – can be said to be diglot.
Ducks are never male. The males of the species are called drakes
The working section of a piano is called the action.
Shoemakers are commonly called cobblers but correctly speaking a cobbler is a shoe repairmen. A shoemaker is a cordwainer – they also made leather bottles and harnesses.
The white part of your fingernail is called the lunula.
The thin line of cloud that forms behind an aircraft at high altitudes is called a contrail.
A depth of 2 fathoms (3, metres) is called a Mark Twain. Originally a fathom was the space reached by with two arms outstretched.
In the early days of film making, people who worked on the sets were called movies. The films were called potion pictures.
