thoraces
Most nouns form their plural by adding "s" to the end of the word.
The plural form for the demonstrative pronoun this is these.
The plural word of delay is delays.
The plural noun is raisins.
The plural of the word brush is brushes. As in "she brushes her hair".
The form thorax it the singular; there are two accepted plural forms: thoraxes or thoraces.
An insect's body is attached to the thorax.
The definition of thoracic is "of or relating to the thorax." There is no noun form of "thoracic" as the word is naturally an adjective, but the thorax is what the word is referrencing.
Fenêtres (fem. plural) means 'windows' in English.
Plankton is plural and its singular form is plankter. However, be aware that the word "plankton" is most often used in its plural as a collective noun.
The plural of the word piano is pianos. Most nouns have an S added to them to make them plural.
Since there is only one Texas, a plural form would not be of any use. But if someday there were a second Texas, it is most likely that "Texases" would be used as the plural. But language sometimes develops in unexpected ways. It is possible that some other form might gain popular acceptance if such a word is ever needed.
The word crises is a plural word; it is the plural form of the word crisis.
Most nouns form their plural by adding "s" to the end of the word.
thorax
The correct word is themselves.Although the word "them" has regained popular use as a singular third-person pronoun of indefinite gender(him/her), the self version is considered incorrect and should be used for the plural "them" only. The word "they" whether considered singular or plural, always uses the plural form of a verb.
The word "tidings" is plural. Although it can also be used in its singular form as "tiding", it is most often used in its plural form.