Most of the headwords with this tag are actually kanji compounds with idiomatic readings (jukujikun / 熟字訓). The word "gikun" (義訓) really only makes sense for describing the readings of single, individual kanji rather than kanji compounds. The JMdict database groups both types together under the "gikun" tag.
I think this is confusing, so it would be better to change the tag to display "special reading" rather than keeping the mostly inaccurate "gikun" label.
Most of the headwords with this tag are actually kanji compounds with idiomatic readings (jukujikun / 熟字訓). The word "gikun" (義訓) really only makes sense for describing the readings of single, individual kanji rather than kanji compounds. The JMdict database groups both types together under the "gikun" tag.
I think this is confusing, so it would be better to change the tag to display "special reading" rather than keeping the mostly inaccurate "gikun" label.