This paper tackles the importance of diachronic variation within the framework of the research dedicated to the lexical field, as well as the implications at the level of practical applications. Two major research perspectives can be distinguished in the field, the traditional one, lacking the adequate technicalities for semantic research, and the modern one, benefiting from the contributions brought about by structural linguistics. The importance of diachronic variation is highlighted for each perspective, next to its impact at the practical level. If in the case of the former perspective the diachronic variation of an onomasiological field is a defining trait, the theoretical framework of the modern perspective excludes the inquiry into a variation of a field, diachronically as much as synchronically. In the final part of the article we focus on the importance of describing, from a modern perspective, a lexical field, at every level of its variation, be it synchronic or diachronic. This leads to a more exact identification of the significance of words belonging to a certain field, within the framework of each version of a historical language. The utility of these results is also exemplified against the background of lexicography.