world / border

boundary / a bounded area or region / a bounded group of people, a society, a world as a social grouping, such as business, celebrities, or finance / the border edge of a thing

border, boundary, limits

nature / spontaneity

natural / spontaneous

naturally / spontaneously / rarely / coincidentally

use one thing for many purposes / work someone hard

(trigonometry, signal processing) sine wave

to use one's head

Kyūjitai form of 現象学 (“phenomenology”)