The word "深入" is formed by directly combining the character "深" (shēn), which means "deep", with the character "入" (rù), which means "enter". The resulting compound semantically conveys the action of entering deeply into a subject, place, or state, as "深" modifies the verb "入" to indicate depth or thoroughness, exemplified in phrases like "深入研究" (deep research) where it denotes penetrating investigation.