単数形名詞でも複数形にもなる名詞

単数形は同じでも、複数扱いで s がつく場合とつかない場合がある単語

単語 複数形の扱い 例文
fish fish … 数や集団としての複数(例: Many fish are swimming)
fishes … 種類ごとに複数を区別するとき(例: There are several fishes in this lake)
Fish are tasty. / There are many different fishes in the aquarium.
aircraft aircraft … 単数も複数も同じ形(sはつかない)
Two aircraft are flying.
species species … 単数も複数も同じ形(sはつくが単数・複数どちらも同じ)
Many species are endangered.
series series … 単数も複数も同じ形(sはつくが単数・複数どちらも同じ)
This TV series is popular. / Several series are available.
sheep sheep … 単数も複数も同じ形(sはつかない)
Ten sheep are grazing in the field.
deer deer … 単数も複数も同じ形(sはつかない)
Three deer are crossing the road.
means means … 単数も複数も同じ形(sはつくが単数・複数どちらも同じ意味)
Various means of transport exist.