Payroll service giant, initially

• Big payroll service co.
• Check-processing company, initially
• Big inits. in check processing
• Big check-printing co.
• Nucleotide involved in photosynthesis
• Big name in payroll
• An ester of adenosine that is converted to ATP for energy storage
• Payroll service initials

Wiktionary Word definitions in Wiktionary
n. (initialism of adenosine diphosphate English)