throw in in WordNet English dictionary

1. give up in the face of defeat of lacking hope; admit defeat
   "In the second round, the challenger gave up"
   drop out  give up  fall by the wayside  drop by the wayside  throw in  throw in the towel  quit  chuck up the sponge 
   
2. to insert between other elements
   "She interjected clever remarks"
   interject  come in  interpose  put in  throw in  inject 
   
3. add as an extra or as a gratuity
   throw in 
   

throw in in English Wiktionary