explain in WordNet English dictionary

1. serve as a reason or cause or justification of
   "Your need to sleep late does not excuse your late arrival at work"; "Her recent divorce may explain her reluctance to date again"
   excuse  explain 
   
2. make plain and comprehensible
   "He explained the laws of physics to his students"
   explain  explicate 
   
3. define
   "The committee explained their plan for fund-raising to the Dean"
   explain