Sometimes arias are called scenas, aria or scena in the singular.
An aria.
Aria
Reduced paid up
That word could be aria.
There is no such thing as an "extended sentence" in grammar. "Extended sentence" is a legal term, not a grammatical term.
A cavatina is a musical term meaning a short simple song that does not have multiple verses or repetitions. A cavatina can be instrumental or vocal and is generally operatic.
That is the proper spelling of the operatic term "aria".
Relations.
Yes.
The term is 'aria-cabaletta'. An example being Violetta's aria from act 1 of La traviata - 'È strano! è strano……Ah! fors e lui' [aria] - 'Sempre libera' [cabaletta].
Apnea
A song from an Opera is known as an Aria - whether it is long or short, however, you can also have an arietta, which is a "little aria" which might also be what you are referring to.