Diurna is a Latin & Italian word relating to `day`. Sometimes refers to: ...
• (n. pl.) A division of Lepidoptera, including the butterflies; -- so called because they fly only in the daytime.
Di·ur'na noun plural [ New Latin , from Latin diurnus belonging to the day.] (Zoology) A division of Lepidoptera , including the butterflies; -- so called because they fly only in the daytime.