In the article, the author considers pairs of such vocabulary units, which in lexicology are usually defined as doublet forms, absolute or complete synonyms. The main idea of the publication is that, by examining such lexical pairs, to show such functional properties of their members, which would make it possible to abandon the characterization of such units as absolutely identical, doublet. On the material of English nouns, marked in special publications and dictionaries as absolute synonyms, we show that in many cases there is a differentiation of members of lexical pairs, leading them beyond the limits of doublet units. It turns out that in the process of functioning, many absolute synonyms not only do not disintegrate, as linguists predict, due to the semantic and formal redundancy of such linguistic forms, but exist for a long time without experiencing a desire for transformation. Apparently, there are factors (reasons) in the language that contribute to the functioning of absolute synonyms. Analysis shows that the set of doublet forms of factors supporting the existence is specific for units of a terminological character, on the one hand, and for absolute synonyms of a commonly used character, on the other.