perspicacity
Concise Oxford English Dictionary © 2008 Oxford University Press:
perspicacious /ˌpəːspɪˈkeɪʃəs/
▶adjective having a ready insight into and understanding of things.
– derivatives
perspicaciously adverb,
perspicacity noun.
perspicaciously adverb,
perspicacity noun.
'perspicacity' also found in these Oxford entries:

