letter challenging someone to a duel

system / series / lineage / family

gender role

(linguistics) "role language": unique language usage serving as a marker of social identity in fictional speech

importance

Kyūjitai form of 生態学 (“ecology”)

ecology

sort, kind, type

kind, sort, type, class, genus, order, family / similar example, parallel

kind, sort, type, the like / a similar thing, parallel / (taxonomy) a conventional grouping that corresponds to a class or an order / (logic) Short for 類概念 (ruigainen).