singly in WordNet English dictionary

1. apart from others
   "taken individually, the rooms were, in fact, square"; "the fine points are treated singly"
   individually  separately  singly  severally  one by one  on an individual basis  individually  separately  singly  severally  one by one  on an individual basis 
   
2. one by one; one at a time
   "they were arranged singly"
   singly  singly