start up in WordNet English dictionary

1. get off the ground
   "Who started this company?"; "We embarked on an exciting enterprise"; "I start my day with a good breakfast"; "We began the new semester"; "The afternoon session begins at 4 PM"; "The blood shed started when the partisans launched a surprise attack"
   start  start up  embark on  commence 
   
2. get going or set in motion
   "We simply could not start the engine"; "start up the computer"
   start  start up 
   

start up in English Wiktionary