d-layer d-day • d. h. lawrence · · · Info · Definitions · Characters · · d-layer · · Text Common · · Latin · · Scripts 7 · · Length 2 · · Syllables Definitions · · · (noun) the lowest region of the ionosphere (35 to 50 miles up) that reflects low-frequency radio waves. Synonyms: D-layer, D region. · · Noun Definition 1 Characters · · - hyphen-minus U+002D a latin small letter a U+0061 d latin small letter d U+0064 e latin small letter e U+0065 l latin small letter l U+006C r latin small letter r U+0072 y latin small letter y U+0079