sandviĉo = pankovertaĵo = sandwich
malĝis = "un-until", aka. "opposite of prior to": after a time/point/location.
We already have various reduced words, and Zamenhof personally said that reducing words is perfectly fine as long as they don't become the same as an already-existing word. The main point of reducing them is either to delete unproductive affixes so that the words become regular (so we don't have to say "sensentema"), or to rid the word of the suffix that was borrowed originally without thinking (an "argument" is a "thing made of 'to argue" = arguaĵo). Thus:
argumento = arguo = an argument
sentema = tema = sensitive, sentient, susceptible
danĝero = danĝo = danger