stumble

[1]	falter , blunder , slip , trip , miss one's footing , stagger , lurch , flounder
[2]	falter , pause , hesitate , trip , slip , blunder
[3]	stumble on/upon , falter , bumble , chance/come/happen on/upon , hit upon , come/run across , find , discover , encounter , (Colloq) bump into
[4]	trip
[5]	hit
[6]	slip up , trip up

[1]	lurch , stagger
[2]	trip , trip-up , misstep