地下鉄
ちかてつ · chikatetsu · JLPT N5 · noun
train
🚇 地下鉄 = ground + below + iron: the iron road under the ground
地下 (chika) means underground, and 鉄 (tetsu) is iron, short for 鉄道 (tetsudō), iron road = railway. So chika-tetsu is literally the underground iron, i.e. the underground railway.
地 — earth 土 + 也 (phonetic)
地 is a semantic-phonetic compound. The left component 土 means 'earth' or 'soil' and gives the meaning, while 也 on the right hints at the pronunciation. Originally referring to the ground or land, it broadened to mean 'place,' 'region,' and 'territory.'
下 — horizontal line 一 + mark below
下 is an indicative character: a long horizontal line represents a reference level, and a shorter stroke placed beneath it points to the area below. The original meaning 'below, down' comes directly from this spatial diagram, and it later extended to verbs like 'descend' and 'lower'.