Answer:
accuracy
Step-by-step explanation:
According to the passage, the thermometer has not been used in a long while and had been abandoned, so the narrator picked it up from the drawer and proceeded to put it under his tongue even though he was not sure of its veracity.
The word veracity as used in this passage means accuracy because the thermometer had not been in use for a long while so he tried using it even though he wasn't sure of its accuracy.