The phrase "most infixed" can be simplified to mean the most commonly used or deeply ingrained. Synonyms for this phrase include "most embedded," "most entrenched," "most ingrained," "most implanted," and "most rooted." These words are useful when describing an idea, belief, or habit that has become deeply ingrained in someone's psyche. A person or society can have deeply ingrained notions about something that are hard to change, and that is where these synonyms come in handy. By using these words, a writer can express the depth of an idea's influence and provide insight into why it may be challenging to change it.