乃至
ないし · naishi · JLPT N1 · conjunction
from...to
乃 — single component, derived from a pictograph
乃 originated as a pictograph, traditionally interpreted as depicting a curved or twisted form, possibly a breath or rope. Over time it lost concrete meaning and became a function word used as a pronoun ('you') in classical Chinese and as an adverb meaning 'thereupon' or 'then'.
至 — arrow 矢 inverted + ground 一
至 is a pictograph showing an arrow (矢) landing point-down on the ground (一), depicting the moment it reaches its target. The original meaning was 'to arrive' or 'to reach,' which extended to 'utmost' or 'extreme' — the point beyond which one cannot go further.