late 14c., "daily, happening every day," from Late Latin diurnalis "daily," from Latin dies "day" + -urnus, an adjectival suffix denoting time (compare hibernus "wintery"). Dies "day" is from PIE root *dyeu- "to shine" (source also of Sanskrit diva "by day," Welsh diw, Breton deiz "day;" Armenian tiw; Lithuanian diena; Old Church Slavonic dini, Polish dzień, Russian den).

From early 15c. as "performed in or occupying one day;" 1620s as "of or belonging to the daytime (as distinguished from nocturnal). Related: Diurnally.

mid-14c., "book of church services," from Anglo-French jurnal, from Old French jornel, "a day; time; a day's travel or work" (12c., Modern French journal), properly "that which takes place daily," noun use of adjective meaning "daily, of the day," from Late Latin diurnalis "daily," from Latin dies "day," from PIE root *dyeu- "to shine."

The meaning "book for inventories and daily accounts" is from late 15c. in English (14c. in French); that of "personal diary" is c. 1600, also from a sense developed in French. Meaning "daily publication" is from 1728. Classical Latin used diurnus for "of the day, by day," and also as a noun, "account-book, day-book."

Initial -d- in Latin usually remains in French, but according to Brachet, when it is followed by an -iu-, the -i- becomes consonantized as a -j- "and eventually ejects the d." He also cites jusque from de-usque.