verb (v)

• break down, literally or metaphorically(verb.motion)

  Synonym:
  break, cave in, collapse, founder, give, give way
  

  source: wordnet30
• to take one's place in a military formation or line(verb.social)

  Example:
  Troops fall in!.
  

  source: wordnet30
• become part of; become a member of a group or organization(verb.social)

  Synonym:
  get together, join
  

  source: wordnet30