The conversation between human and AI assistant.
[|Human|] Identify the part of speech for the word "abstract" in the sentence: "The abstract concept is difficult to define."
[|AI|] In the sentence "The abstract concept is difficult to define," the word "abstract" is an adjective.
[|Human|] 
Identify the part of speech for the word "abstract" in the sentence: "The abstract concept is difficult to define."