Source : Webster's Revised Unabridged Dictionary (1913)

Sinistrously \Sin"is*trous*ly\, adv.
   1. In a sinistrous manner; perversely; wrongly; unluckily.

   2. With a tendency to use the left hand.

            Many, in their infancy, are sinistrously disposed,
            and divers continue all their life left-handed.
                                                  --Sir T.
                                                  Browne.