"Gat behind" is a colloquial phrase that means to lag behind or fall behind in a group or activity. Some common synonyms for "gat behind" include lagging, trailing, falling back, slowing down, and being left behind. Other synonyms might include being outpaced, outdistanced, or left in the dust. These terms all describe the same concept of someone or something being slower or less proficient than others around them. While the phrase "gat behind" is not commonly used in formal writing or speech, its synonyms can be used in a variety of contexts to describe the same situation.