This paper deals with some criteria of stylistic marking of the words or their meanings as colloquial or vernacular in academic explanatory dictionaries starting with Ushakov Dictionary and ending with the latest lexicographic works, such as Large Dictionary of the Russian Language ed. by S.A. Kuznetsov, Active Dictionary of the Russian Language ed. by Ju.D. Apresjan, Academic Explanatory Dictionary of the Russian Language ed. by L.P. Krysin, et al. The parameters of the colloquial speech and vernacular, which are formulated explicitly in the prefaces of the dictionaries, are based on the speech usage and on the language norm (in particular, the use in live and mainly oral speech, as well as compliance / non-compliance with the norms of literary use). Analyses of stylistic marks “colloquial” and “vernacular” in academic explanatory dictionaries shows that, in addition to these characteristics, lexicographers were also guided by some implicit criteria, such as: 1) figurative (metaphorical, metonymic); 2) emotional-evaluative connotation; 3) presence of the word neutral lexical equivalent. The article discusses some controversial cases of stylistic marking of the words as colloquial and vernacular in academic explanatory dictionaries based on these criteria.