Nippier is the comparative form of nippy.
Weather that's nippier is colder and more biting: It's nippier this morning than yesterday.
A person who's nippier moves more quickly and nimbly.
In British usage, a nippier car handles with greater agility.
1. colder — chilly, Moderately cold; frosty (Cold or unwelcoming); crisp (Firm and breakable); biting (Harshly critical or cold); brisk · raw · sharp · wintry · frigid · icy · cool · bitter · freezing · cutting
2. quicker — faster, With more velocity; swifter (More rapid in motion); speedier (More rapid, quicker); zippier (More lively and brisk); snappier · hastier · livelier · brisker · nimbler · sprightlier · peppier · racier · prompter · agile
Opposites
TEMPERATURE SENSATIONnippier ≠ warmer Higher in temperature; balmier · milder · toastier · muggier · stuffier
SPEED/AGILITYnippier ≠ slower Reduced in speed; clunkier · heavier
speed/quicknessnippier ≠ slower Reduced in speed; pokier · clumsier