1. (serious usage) used to describe someone that is observant, it means to see through, or see clearly. Someone who is descibed as perspicacious understands what they observe and usually sees through the lies and facades that others use to hide behind.
2. (common usage) Generally this word is used when one wishes to sound like a know-it-all, or used sarcastically to describe someone who acts like a know-it-all.
Common words used with this: Pompous windbag
1. "I tried to tell Tom that I just wanted to be friends, but he knew I thought he was an ass... he's so perspicacious." -Julia
2. "Wow... Tom knew JUST what Julia meant, didn't he? He's pretty perspicacious, isn't he? .......the dumbass, pompous windbag." -Julia's angry friend