体 is very productive: 身体 (body), 体育 (sports), 具体 (concrete), 字体 (font), 整体 (overall). A rare second reading tī is bound to 体己 (private savings; intimate), the only word that uses it; everywhere else the reading is tǐ.
Person radical on the left, the indexing semantic. 体 is the simplified form of 體, replacing the original phonetic with the clearer 本. The body belongs to a person, so 亻 anchors it in the human-body family: 你, 他, 休 (rest).
Right component is 本 'root, foundation' (a 木 tree with a mark on its base). The combination reads as a meaning gloss: a person's root is the body. The sound has drifted (běn is not tǐ), so 本 here works as a semantic mnemonic rather than a true phonetic; the original 體 carried the sound through a different element.
