Lightning is one of those pet names that arrives as a fait accompli: you see the puppy move for the first time and the name is already there. It's purely aspirational in the sense that speed is being named rather than guaranteed, but dogs named Lightning do tend to be dogs whose owners watched them demolish a backyard and reached for the first word that covered the situation.
The Speed Name Tradition
Lightning sits in a cluster of speed and weather names: Thunder, Storm, Flash, Lightning. The Pixar connection, Lightning McQueen from the Cars franchise (2006-present), has kept it in cultural circulation for two decades. Greyhounds and Vizslas are natural fits.
Sound and Weight
LIGHT-ning is two syllables with a T that gets swallowed in rapid speech, sounding faster when said quickly. As a recall name it's somewhat long for high-distraction environments, but the first syllable LIGHT functions as an effective short form.
Counter-Reading: Registry Fragmentation
Lightning at rank 2077 with 47 records splits with Lightning McQueen (some owners register the full name) and potentially with Lightnin' in certain communities. The actual population of dogs called Lightning in some form is larger than this tier suggests. Browse other weather and speed pet names.