bedrock

Từ điển Oxford Advanced Learner 8th

bed·rock [bedrock bedrocks] BrE [ˈbedrɒk] NAmE [ˈbedrɑːk] noun
1. singular a strong base for sth, especially the facts or the principles on which it is based
•The poor suburbs traditionally formed the bedrock of the party's support.
•Honesty is the bedrock of any healthy relationship.
2. uncountable the solid rock in the ground below the loose soil and sand

Example Bank:
•The poor suburbs traditionally formed the bedrock of the party's support.