Meaning unknown. Used to modify ame/ama ‘heaven’, sora ‘sky’ and things connected with them such as: tuki ‘moon’, pi ‘sun’, piru ‘daytime’, ame ‘rain’, yuki ‘snow’, kasumi ‘haze’, posi ‘star’, pikari ‘light’ and yo ‘night. Also for katura ‘Katsura (tree)’, miyako ‘capital’, kagami ‘mirror’. One theory is that it derives from pi sasu kata ‘the direction from which the sun shines’, while the characters used to write it suggest the eternal and/or far-reaching nature of the heavens.