Final answer:
The word 'fastidious' in the sentence is an adjective that describes the painter.
Step-by-step explanation:
In the sentence, the word fastidious is an adjective. Adjectives are words that describe or modify nouns or pronouns. In this case, 'fastidious' describes the word 'painter', indicating that the painter is extremely attentive to detail and particular about his work.
Learn more about Parts of speech