The word "忠于" (zhōng yú) is formed by combining the character "忠", meaning "loyalty" or "devotion", with the preposition "于", which means "to" or "toward". This structure creates a verb phrase meaning "to be loyal to", where "忠" provides the core meaning of faithfulness and "于" grammatically directs that loyalty toward a specific object, person, or cause, effectively turning an abstract quality into an actionable and directed commitment.