English boasts numerous words to convey aspects of friendship. Some are Germanic in origin and others, Latin.
An early Old English word for friend was freond. The Beowulf poet tells us that Heorot (Hrothgar’s hall) was filled with friends: Heorot innan wæs freondum afylled.
The opposite of Old English freond was feond: “enemy.” In modern English, the word that initially referred to a human foe has developed into the word fiend: “an evil spirit.”
In the most general sense, a friend is “a person with whom one has developed a close and informal relationship of mutual trust and intimacy.” In specific contexts, friend can refer to an ally in war, the supporter of a cause, or, with a capital, a Quaker (member of the religious Society of Friends).
The adjective for friend is friendly: “characteristic of or befitting a friend or friends; that expresses or is indicative of friendship or a kind and helpful attitude.” Friendly is also used as a noun to mean “an ally.” In US colonial times, “a friendly” was an indigenous person who was on peaceful terms with the settlers. In modern military parlance, friendlies are troops on the side of one’s own forces or those of one’s allies.
The abstract noun for the state of being a friend is friendship.
The use of friend as a verb to describe the adding of a person to a list of social media contacts (dating from 2004) is still regarded as a barbarism by many English speakers, but friend was used as a verb as early as the 13th century. For several centuries, the verb befriend was in more common use, but the modern use of friend and unfriend as verbs is idiomatic. The use of friend in the context of social media does not negate the usefulness of befriend to refer to a genuine personal contact in which one person helps another.
The Latin word for friend, amicus (plural, amici), has given English several additional words to convey cordial feelings:
amiability noun: quality of being friendly
amiable adjective: friendly
amiably adverb: in a friendly manner
amicability noun: friendliness
amicable adjective: done in a friendly spirit
amicably adverb: in a friendly manner
amity noun: friendly relations, especially of a public character
The legal term amicus curiae (plural, amici curiae), literally “friend of the court,” refers to a person or group that is not a party to a lawsuit, but has a strong interest in the matter. An amicus curiae will petition the court for permission to submit a brief in the action with the intent of influencing the court’s decision. A brief is a written statement that explains one side’s legal and factual arguments. The brief submitted to the court by an amicus curiae is called “an amicus brief.”