A girl is a female human from birth through childhood and adolescence to attainment of adulthood when she becomes a woman. The term girl may also be used to mean a young woman, and is often used as a synonym for daughter.
The English word girl first appeared during the Middle Ages between 1250 and 1300 CE and came from the Anglo-Saxon words gerle (also spelled girle or gurle). The Anglo-Saxon word gerela meaning dress or clothing item also seems to have been used as a metonym in some sense.
Girl has meant any young unmarried woman since about 1530. Its first noted meaning for sweetheart is 1648. The earliest known appearance of girl-friend is in 1892 and girl next door, meant as a teenaged female or young woman with a kind of wholesome appeal, dates only to 1961.
The word girl is sometimes used to refer to an adult female, usually a younger one. This usage may be considered derogatory or disrespectful in professional or other formal contexts, just as the term boy can be considered disparaging when applied to an adult man. Hence, this usage is often deprecative. It can also be used deprecatively when used to discriminate against children ("you're just a girl").
An aria ([ˈaːrja]; Italian: air; plural: arie [ˈaːrje], or arias in common usage, diminutive form arietta [aˈrjetta]) in music was originally any expressive melody, usually, but not always, performed by a singer. The term became used almost exclusively to describe a self-contained piece for one voice, with or without orchestral accompaniment, normally part of a larger work. The typical context for arias is opera, but vocal arias also feature in oratorios and cantatas, sharing features of the operatic arias of their periods.
The term, which derives from the Greek and Latin 'aer' (air) first appeared in relation to music in the 14th century when it simply signified a manner or style of singing or playing. By the end of the 16th century, the term 'aria' refers to an instrumental form (cf. Santino Garsi da Parma lute works, 'Aria del Gran Duca' ). By the early 16th century it was in common use as meaning a simple setting of strophic poetry; melodic madrigals, free of complex polyphony, were known as madrigale arioso.