Etymology and terminology
The English word breast derives from the Old English word brēost (breast, bosom) from Proto-Germanic *breustam (breast), from the Proto-Indo-European base bhreus– (to swell, to sprout). The breast spelling conforms to the Scottish and North English dialectal pronunciations. The Merriam-Webster Dictionary states that "Middle English brest, [comes] from Old English brēost; akin to Old High German brust..., Old Irish brú [belly], [and] Russian bryukho"; the first known usage of the term was before the 12th century.A large number of colloquial terms for breasts are used in English, ranging from fairly polite terms to vulgar or slang. Some vulgar slang expressions may be considered to be derogatory or sexist to women. Evolutionary development
Humans are the only mammals whose breasts become permanently enlarged after sexual maturity (known in humans as puberty). The reason for this evolutionary change was unknown. Several hypotheses have been put forward:
A link has been proposed to processes for synthesizing the endogenous steroid hormone precursor dehydroepiandrosterone which takes place in fat rich  regions  of the body like the buttocks and breasts. These contributed to human brain development and played a part in increasing brain size. Breast enlargement may for this purpose may have occurred as early as Homo ergaster (1.7-1.4 MYA). Other breast formation hypotheses may have then taken over as principal drivers.It has been suggested by zoologists Avishag and Amotz Zahavi  that the size of the human  breasts can be explained by the handicap theory of sexual dimorphism.
In a few Western countries and regions female toplessness at a beach is acceptable, although it may not be acceptable in the town center.Social attitudes and laws regarding breastfeeding in public vary widely. In many countries, breastfeeding in public is common, legally protected, and generally not regarded as an issue. However, even though the practice may be legal or socially accepted, some mothers may nevertheless be reluctant to expose a breast in public to breastfeed due to actual or potential objections by other people, negative comments, or harassment. It is estimated that around 63% of mothers across the world have publicly breast-fed. Bare-breasted women are legal and culturally acceptable at public beaches in Australia and much of Europe. Filmmaker Lina Esco made a film entitled Free the Nipple, which is about "...laws against female toplessness or restrictions on images of female, but not male, nipples", which Esco states is an example of sexism in society. Sexual characteristic
In some cultures, breasts play a role in human sexual activity. In Western culture, breasts have a "...hallowed sexual status, arguably more fetishized than either sexs genitalia". Breasts and especially the nipples are among the various human erogenous zones. They are sensitive to the touch as they have many nerve endings; and it is common to press or massage them with hands or orally before or during sexual activity. During sexual arousal, breast size increases, venous patterns across the breasts become more visible, and nipples harden. Compared to other primates, human breasts are proportionately large throughout adult females lives.