There are two groups of causes of semantic change: extralinguistic (historical) and linguistic factors.
Extralinguistic causes
In nation's social life, in its culture, knowledge, technology, arts, changes occur in all spheres of human activities. Newly created objects, new notions
and phenomena must be named. There are two main ways for providing new names for newly created notions: making new words, and borrowing foreign ones. There is one more way: it is applying some old word to a new object or notion.
E.g.: the word carriage had and has the meaning of a vehicle drawn by horses. But with the first appearance of railways in England, it received a new meaning - a railway car; pen —> feather, metal, ball pen; sail - плавать под парусами —> плавать (о любом судне).
Some changes of meaning are due to purely linguistic causes, i.e. factors acting in the language system. Linguistically speaking, the development of new meanings, and also a complete change of meaning, may be caused by the influence of other words, mostly of synonyms.
The process of changing the meaning of words due to collision of synonyms is called discrimination of synonyms. Other examples of discrimination of synonyms: land (страна, земля) - country (Fr.) - страна, stool (стул, табурет) - chair (Fr.) - стул, meat (пища, мясо) - food (Fr.) - пища, deer (животное любое, олень) - animal (Fr.) животное.
The next linguistic process is ellipses - the omission of a word in a phrase and the meaning of the whole word-group is transferred to the remaining component. E.g.: the OE verb steorfan (to starve) meant to perish. When the verb to die was borrowed from the Scandinavian, these two synonyms, which were very close in their meaning, collided, and, as a result, to starve gradually changed into its present meaning: to die (or suffer) from hunger. Already in the 14th century the word hunger gradually stopped to be used in this phrase and the verb itself got this meaning.
Other examples of ellipses: a sit-down (demonstration); a daily (newspaper); a monthly (magazine); a taxi (cab).
The third linguistic cause is linguistic analogy. It is found out that if one of the members of a synonymic set gets a new meaning, other members of this set change their meaning accordingly. E.g., verbs synonymous with catch (grasp, get, etc.) got the meaning to understand.