Other forms: advertising, advertised, advertises
To advertise is to tell the public about something you want to sell. Or about a job you want filled.
It takes for when you are looking for something, so advertising for a cleaner means placing a notice. It works without an object too, since a company advertises. There is a useful figurative sense about discretion, and not advertising the fact means keeping quiet about it, which is a very British way of describing modesty. British English spells it with an s in both countries, since it is not one of the -ize verbs.
To advertise was to warn. Middle French avertir meant to give notice or to warn somebody, and the word took up the business of selling only much later.
Middle French
advertir
Anglo-Norman
advertir — to inform
Middle English
advertisen
English, today
advertise
Built from
From Middle English advertisen, from Anglo-Norman advertir (“to inform”), avertir, Middle French advertir, avertir (“to warn, give notice to”), with the French -iss- infix assimilated to -ise, -ize and probably influenced by the noun advertisement. Compare also advert.
Etymology from Wiktionary, CC BY-SA