Let down等于什么

let down常见释义放下[词典]使失望; 使沮丧; 辜负; 使美中不足; 使差强人意; 使不理想; 给（轮胎等）放气; 例句:He let down the tailgate so the dog could jump out.他放下后背门，好让狗跳出来。