The word "bum" is generally considered to be an informal term that refers to the buttocks or someone who is homeless or lazy. However, there are several synonyms that can be used in its place, depending on the context of the sentence. Some possible synonyms for "bum" include "rear end," "butt," "backside," "derriere," "homeless person," "tramp," "vagabond," "drifter," and "hobo." Each of these words can convey a slightly different connotation, with "rear end" being the most neutral and "hobo" having a more negative connotation. Overall, it's important to choose the right synonym for the situation to avoid confusion or offense.