f layer f clef • f number · · · Info · Definitions · Characters · · f layer · · Text Common · · Latin · · Scripts 7 · · Length 3 · · Syllables Definitions · · · (noun) the highest region of the ionosphere (from 90 to 600 miles up) which contains the highest concentration of free electrons and is most useful for long-range radio transmission. Synonyms: Appleton layer, F layer, F region. · · Noun Definition 1 Characters · · space U+0020 a latin small letter a U+0061 e latin small letter e U+0065 f latin small letter f U+0066 l latin small letter l U+006C r latin small letter r U+0072 y latin small letter y U+0079