What is the meaning of bear down?

verb

• Exert a force with a heavy weight.
  • usage: "The snow bore down on the roof"
  • synonyms: drag down, bear down on, press down on, weigh down
• Contract the abdominal muscles during childbirth to ease delivery.
  • synonyms: overbear
• To make a rush at or sudden attack upon, as in battle.
  • usage: "he saw Jess charging at him with a pitchfork"
  • synonyms: charge
• Exert full strength.
  • usage: "The pitcher bore down"
• Pay special attention to.
  • usage: "The lectures bore down on the political background"
• Exert a force or cause a strain upon.
  • usage: "This tax bears down on the lower middle class"