Etymology: The centre character (looking a lot like an elbow) used to mean flaming arrow, with the connotation of illuminating an area.
Adding the character for roof lent the original meaning of spacious building, which in time became wide / spacious.
Mnemonic: SPACIOUS BUILDING HAS PLENTY OF ELBOW ROOM
広島 (Hiroshima) name of city
広告 (koukoku) advertisement
(Based upon Henshall, 1998)