look up vs weaken

look up

verb
  • To reconnect or meet with someone that one used to know. 

  • To obtain information about something from a reference book. 

  • To have better prospects. 

  • To enter a query into a database or search engine. 

  • Used other than figuratively or idiomatically: see look, up. 

  • To obtain, or seek to obtain, information about something. 

weaken

verb
  • To make weaker or less strong. 

  • To become weaker or less strong. 

How often have the words look up and weaken occurred in a corpus of books? (source: Google Ngram Viewer )