payroll vs payroll department

payroll and payroll department both are nouns.

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

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

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

payroll (noun)	payroll department (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