Jilly is the diminutive of Jill, itself a medieval short form of Gillian (from the Latin Juliana), compressed into a two-syllable nickname that sounds inherently cheerful. For a female pet, it's the kind of name that lands as warm and immediate without requiring any cultural context to appreciate.
The Nickname-as-Name Register
Jilly belongs to the category of diminutives that feel complete as standalone names: Millie, Lulu, Coco, Winnie. These work particularly well for pets because they never feel overly formal and they call easily. The human name Jillian is the formal root; Jilly is what you'd call someone you like immediately. That quality translates to pet naming without any adjustment required.
Breed and Temperament Fit
Jilly suits small-to-medium female dogs with an outgoing personality. Cocker Spaniels and Cavalier King Charles Spaniels wear it naturally, breeds associated with warmth and sociability. For cats, a tortoiseshell with an assertive personality is a natural Jilly.
The Counter-Reading: Almost Too Breezy
Jilly is so upbeat that it can feel slightly one-dimensional. It doesn't carry much narrative weight or literary depth — it's a name that does one thing and does it well. For owners who want a name with more layers, Josephine or Julia offer similar phonetic terrain with more formal backstory available.