Wordnet 3.0
ADJECTIVE (3)
1. 
 occurring or existing at the same time or having the same period or phase; 
- Example: "recovery was synchronous with therapy"- Jour.A.M.A.- Example: "a synchronous set of clocks"- Example: "the synchronous action of a bird's wings in flight"- Example: "synchronous oscillations"[syn: synchronous, synchronal, synchronic]
2.  concerned with phenomena (especially language) at a particular period without considering historical antecedents; 
- Example: "synchronic linguistics"
3.  (of taxa) occurring in the same period of geological time; 
WordNet (r) 3.0 (2006):
synchronic
    adj 1: occurring or existing at the same time or having the same
           period or phase; "recovery was synchronous with therapy"-
           Jour.A.M.A.; "a synchronous set of clocks"; "the
           synchronous action of a bird's wings in flight";
           "synchronous oscillations" [syn: synchronous,
           synchronal, synchronic] [ant: asynchronous]
    2: concerned with phenomena (especially language) at a
       particular period without considering historical antecedents;
       "synchronic linguistics" [ant: diachronic, historical]
    3: (of taxa) occurring in the same period of geological time