Grammatical category is almost always encoded (implicitly or explicitly) in all lemmas in dictionaries, regardless of their type (monolingual/multilingual, learner/general user etc.). Grammatical category assignment, however, is not an easy task: central to the problem is the issue of discreteness vs. continuity of categories, which will be raised in the paper in relation to sentential adverbs. Sentential adverbs are those that that are "peripheral to the sentence structure" (Leech & Startvik, 1975). They are found in the linguistics literature under a variety of names: discourse markers, conjuncts, disjuncts, style markers, particles, textual adverbs etc. This variety shows the problems (a) in drawing the boundaries between sentential adverbs and their contiguous categories (other adverbs and conjunctions, primarily), and (b) in specifying the criteria for putting together under this umbrella term different types of adverbs. The paper will include theoretical discussions drawn from relevant linguistic and corpus-based analyses and focus on the lexicographical implications thereof, i.e. the way this fuzziness is reflected in lexicography, as evidenced in selected printed Modern Greek and English dictionaries. The choices made in encoding sentential adverbs, both as regards macrostructural and microstructural elements, will be presented and critically evaluated in order to show advantages and disadvantages of adopted solutions.