The componential and contextual analyses as well as the data of modern synonymic dictionaries helped to identify the semantics of the preposition v chasti and the set of its nearsynonyms; its common semes have been found equally actualized in contexts and valencies of the same type. The composition and conditions for the realization of the synonymous prepositional meanings were established from explanatory dictionaries. The complex usage of contextual and componential analyses made it possible to reveal the semes inherited by the actual meanings of the preposition v chasti from the motivating meanings of the noun chast ' (part) and to determine its semantic range.
It has been found that the polysemy of the preposition v chasti is predetermined by the inherited polysemy of its word base. Six systemic meanings of the preposition v chasti have been discovered in the primary (oral) and secondary (shorthand notes) official speech as well as three potential meanings, then their typical valency has been determined.
The results of the research allow concluding that the preposition v chasti in all its meanings functions as follows: 1) enters into synonymous relations with non-derivative and with other derived prepositions of the genitive case and is semantically identified in this synonymy; 2) is motivated by meanings 1 and 5 of the nominal base chast' in their polysemous diversity; 3) is motivated by either explicit or implicit semantic components of the nominal base which are determined at identification levels 2-4; 4) retains the connection with the general semantic feature indicating the correlation to some sphere, group, variety of objects, to some of their classes and to the inherited semantics of the motivating noun chast.
Thus, the sphere of usage of the preposition v chasti in informal and formal business speech appears to be much richer than that indicated by lexicographic sources. This extension of the meanings of the function word derivatives in active discourses reflects the current general semantic processes and deserves a more thorough study.