海路
かいろ · kairo · JLPT N1 · noun
path
🚢 海 (kai, sea) + 路 (ro, road) = a road on the sea = sea route
The same 路 (ro, road or route) appears in 道路 (dōro, road). Swap 海 for 道 and you get a land route, so the pattern is 'where' + 路.
海 — water radical 氵 + 每 (phonetic)
海 is a phono-semantic compound. The 氵 (water) radical signals the meaning—a vast body of water—while 每 supplies the sound. Originally referring to the sea or ocean, it later extended figuratively to mean 'vast' or 'a great quantity,' as in 人海 (a sea of people).
路 — foot 足 + each 各 (phonetic)
路 is a semantic-phonetic compound. The foot radical 足 on the left signals meaning related to walking or travel, while 各 on the right hints at the ancient pronunciation. Originally referring to a road traveled on foot, it broadened to mean 'road, path, route' in general.