fundamental

Forming a necessary base or core; of central importance; (plural noun) the essential principles of something.

• fundamentally/ˌfʌndəˈmɛntəli/(adv)根本上；从本质上
• fundamentalism/ˌfʌndəˈmɛntəlɪzəm/(n)原教旨主义
• fundamentals/ˌfʌndəˈmɛntəlz/(n pl)基本原理

• fundamental change
• fundamental principle
• fundamentally different
• a fundamental shift
• back to basics
• grasp the fundamentals
• fundamental right
• fundamental flaw

1. 1.There is a fundamental difference between the two approaches that goes beyond surface-level style preferences.
2. 2.Before diving into the advanced material, it's important to have a solid grasp of the fundamentals.

• basic/ˈbeɪsɪk/— forming the foundation
• core/kɔː/— central and essential
• essential/ɪˈsɛnʃəl/— absolutely necessary; most important

from Latin "fundamentum" = foundation, from "fundare" (to found), from "fundus" (bottom)