如一 (rú yī) means 'consistent, the same, unchanged' and is used in literary or set phrases like 始终如一 (consistent from start to finish). Unlike 一致 (yī zhì), which describes agreement among people or opinions, 如一 emphasizes continuity over time or alignment between inner and outer. 一贯 (yī guàn) is an adjective meaning 'consistent as a habit or policy', while 如一 is a verb-like element that always follows a noun or phrase.