"Siz" is a relatively uncommon word that is typically used in dialectal English to mean "right away" or "immediately." While it might not be the most recognizable term, there are still a number of synonyms that can be used in its place. Some synonyms include "at once," "right now," "this instant," "in a jiffy," "in a trice," "straightaway," "posthaste," "pronto," "tout de suite," "stat," and "asañas possible." Each of these terms can be used interchangeably with "siz," depending on the context and tone of the conversation. Regardless of the word you choose, the overall meaning will remain the same - an urgent need for action.