English to English

verb (v)

• make longer(verb.change)

  Example:
  Lengthen this skirt, please.
  

  source: wordnet30
• become long or longer(verb.change)

  Example:
  In Spring, the days lengthen.
  

  Antonym:
  shorten
  

  source: wordnet30
• To extent in length; to make longer in extent or duration; as, to lengthen a line or a road; to lengthen life; -- sometimes followed by out.(verb)

  source: webster1913
• To become longer.(verb)

  source: webster1913