The word-stock of any language is never stable, but is constantly changing. These changes may be of different kinds. Sometimes the vocabulary may be enriched by words from other languages due to the influence between nations or other reasons. Sometimes new meanings are added to the one concrete word. That is why we have so many polysemantic words.
There are two principal approaches in linguistic science to the study of language material, the nominal synchronic and the diachronic approach. The synchronic approach is concerned with the vocabulary of a language as it exists at a given time, for instance, at the present time. As for diachronic approach it deals with the changes and the development of vocabulary in the course of time. These two approaches help us to learn origin of words, changes through the history, analyze old and newly acquired meanings, find the reason-why this or that meaning appeared and so on.
Every word has its etymology, primary origin, but due to the different changes sometimes the original meanings are blurred or completely lost.
If we analyze the word "friend" in the diachronic and synchronic planes, we will notice that original meaning of the word has been maintained. This is one of the few words which preserved original meaning. "" Friend "has Germanic origin and in the old English it has different spelling -" freond ", but the same meaning, as it has now.
According to the original meaning "friend" means to have a person you trust the most, share your joy and troubles, have much in common etc. So this meaning is the same in modernity, but several other meanings are also added.
The process of increasing the amount of meaningings of the word "friend" began in the middle English period. In the middle English the connotational meaning was added and "friend" denoted "a person, who supports, sympathizes with or patronizes a group, cause or movement.
The word "friend" mostly has positive connotational meaning if it is not used in ironical sense. It is used quite often by different groups. Eg religious groups use it as a wide-spread form of addressing (a friend's meeting). In legislative profession the word is used to denote people of these profession (my learned friend-a young lawyer is addressed such way in a court).
In the late middle ages the word acquired another new meaning-romantic partner. As a result the words "girl-friend", "boy-friend", "man-friend", "lady-friend" appeared in the language.
We can single out briefly the main contextual meanings in which the word "friend" is used:
1) a person you like, know well and is not a member of your family
2) a person supporting or patronizing organizations or movements
3) a person having the same views and opinions as you. Eg you are among friends here-you can act freely
4) in parliament or in a court. Eg my favorite friend, my noble friend etc.
There are many idioms or phraseological units using the word "friend". Eg "a friend in need is a friend indeed", "have a friend in high places", which means to know influential people, who can support you. "fast-friends" means very good and devoted friends. "fair weather friends" etc.
It is noteworthy that "friend" is somehow a symbol of social networks. Eg let's take one of the popular networks, Facebook. The people in our list are called "friends". In fact we may not have very close contact with them. This may be considered as another modification of the meanings of the word "friend".