There are various synonyms for the phrase "begin a fall," each with a slightly different connotation. One option is "tumble," which suggests a loss of balance or control. Another is "descend," which implies a gradual decline or lowering. "Plunge" indicates a sudden and steep drop. "Slip" suggests a brief, unintentional loss of footing. "Topple" conveys a sense of tipping over or collapsing. "Drop" is a more general term that can refer to any downward movement. All of these synonyms can be used to describe the start of a physical fall or a decline in a metaphorical sense, such as the beginning of a company's financial downfall.