Kyūjitai form of 生態学 (“ecology”)

an ecosystem (system of an ecological community and its environment)

(weaponry) a Japanese hand weapon or climbing tool, whereby metal hooks are strapped to the back of the forearm and hand

fishing hook, fishhook - a barbed hook, usually metal, used for fishing.

a corner bracket, either of the pair of brackets 「」, serving as a quotation mark in Chinese and Japanese orthography

perfectionism

(computing theory) Turing complete

perfect and without blemish; flawless

(number theory) perfect number, a positive integer that is equal to the sum of its positive divisors, excluding the number itself

(mathematics) panmagic square