• pil‧lar [countable]

• 1
• a) a tall upright round post used as a support for a roof or bridge:
• Eight massive stone pillars supported the roof.
• b) a tall upright round post, usually made of stone, put up to remind people of an important person or event
• 2

   pillar of society/the community/the church etc

  somebody who is an important and respected member of a group, and is involved in many public activities:
• Mr Fitzwilliam had been seen as a pillar of the community.
• 3 a very important part of a system of beliefs or ideas
• pillar of
• One of the pillars of a civilized society must be that everyone has equal access to the legal system.
• 4

   be driven/pushed from pillar to post

  to have to go from one person or situation to another without achieving much or being able to settle:
• The poor kid has been pushed from pillar to post.
• 5

   be a pillar of strength

  if someone is a pillar of strength, they are there to give you help and support at a difficult time:
• Christine's been a pillar of strength to me.
• 6

   pillar of dust/smoke/flame etc

  a tall upright mass of dust, smoke, flame etc

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.