脊 (jí) is a bound morpheme meaning 'spine, backbone, or ridge'. It cannot stand alone as a word; you must use it inside a compound like 山脊 (mountain ridge), 脊骨 (spine bone), or 脊梁 (backbone). Note that the pronunciation given here is jí (second tone), while the more common reading in modern Mandarin is jǐ (third tone) — this may be a data inconsistency.