noun
prop word
A linguistics term for a dummy word or placeholder used to satisfy syntactic requirements without adding meaning, such as English 'it' in 'It is raining'.
英語の「It is raining」の「it」は支柱語の一例です。
The 'it' in English 'It is raining' is an example of a prop word.
Compound of 支柱 (support, prop) and 語 (word), likely a calque from English 'prop word'.