Each; per item; distributed or given to each individual person or thing separately (usually 'a piece' or 'apiece').
From 'a piece,' where 'a' combines with 'piece' meaning 'one part.' This phrase became standardized as a single adverb meaning 'each one' by the 16th century.
When you give cookies apiece to your friends, you're using an old phrase that literally means 'one piece each'—and the spelling shows exactly how the words merged together!
Complete word intelligence in one call. Free tier — 50 lookups/day.