0
He felt its presence, as insubstantial as a flurry of dust motes caught in a beam of moonlight.
His alibi was insubstantial, without supporting evidence.
Insubstantial means with no substance. Here are some sentences.
I was hungry because I had not eaten a meal in 10 hours, only an insubstantial snack.
unsubstantiated
Because it is insubstantial.
In an insubstantial or weak manner