Individually (3)
(Other definitions for apiece that I've seen before include "Per person" , "for everyone" , "For or by each one of group" , "A head" .)
'individually' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for each that I've seen before include "...per head" , "Ache (anag.)" , "Every single one, person or thing" , "Every - apiece" , "every individual" .)
'individually' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for per that I've seen before include "For each or every" , "Preposition meaning for each" , "According to" , "Preposition indicating by means of" .)
'individually' is the definition.
(synonyms)
This is all the clue.
(Other definitions for one by one that I've seen before include "not appearing all at once?" , "Sequentially" , "royal autobiography?" , "Eleven" , "How queue's served" .)