Holla in Hamlet

When I first began to read Hamlet, I was taken aback when on line 19 in Act 1, Marcellus says: "Holla Barnardo." I did not even know what this word was, so I tried pronouncing it to myself. However, my pronunciation sounded awfully like the Spanish word hola. Although I have not taken Spanish for several years, I was still fairly certain that hola had one l, that my version of the text was not the Spanish edition, and that people in Denmark do not speak Spanish.  To this end, I began to investigate what this mysterious word was. I looked on dictionary.com to see if I could find a pronunciation but I was unsuccessful. Eventually, I resorted to downloading and listening to the audiobook of that specific section of the text. What I heard astonished me. This word sounded like the slang English word that I had heard used in dramatic fashion on T.V. and this confounded me. Was a word that has seen much usage as a slang term nowadays really descended from a word used by Shakespeare? As it turns out, yes. Going back to the dictionary, I learned that similar to its usage today, holla actually is an informal form of greeting. Thus, its use is entirely plausible in Hamlet as it is a form of greeting used by Marcellus to address Barnardo. Nevertheless, I was still shocked to find such colloquial language in one of the most famous plays in the world. I guess it shows that the meaning and context of a word can really change through the passage of time.