payroll department vs payroll

payroll department and payroll both are nouns.

Word	Noun	Adjective	Verb	Adverb
payroll department	Yes	No	No	No
payroll	Yes	No	No	No

As nouns, payroll department and payroll are synonyms defined as:

payroll department and payroll: the department that determines the amounts of wage or salary due to each employee

payroll department (noun)	payroll (noun)
the department that determines the amounts of wage or salary due to each employee	the department that determines the amounts of wage or salary due to each employee
	a list of employees and their salaries
	the total amount of money paid in wages