Identify the part of speech for the word "abstract" in the sentence: "The abstract concept is difficult to define."
In the sentence "The abstract concept is difficult to define," the word "abstract" is an adjective.
Complete the following task based on the instruction and optional input provided.### Instruction:
Identify the part of speech for the word "abstract" in the sentence: "The abstract concept is difficult to define."

### Output:
In the sentence "The abstract concept is difficult to define," the word "abstract" is an adjective.