Sludging refers to the act of moving through something heavy or sticky, typically with difficulty or resistance. Synonyms for this word can include trudging, plodding, slogging, or laboring. These words all convey a sense of exertion, effort, and struggle, which are closely related to the idea of sludging. Other possible synonyms might include wading, struggling, or pushing, depending on the context and the specific nuances of the situation. No matter which word is used, the sense of weightiness, resistance, and difficulty is likely to be a key element of the underlying meaning.