"remoteness," 1540s, from Latin longinquitas "length, extent, duration," from longinquus "long, extensive, remote, distant," from longus (see long (adj.)) -inquus.
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for longinquity
I think the proximity of wine a matter of much more importance than the longinquity of water.Crotchet Castle
Thomas Love Peacock