IPA: /ˈdʒʌmpɪə/
KK: /ˈdʒʌmpɪər/
More easily startled or nervous than usual.
The cat was jumpier than ever after hearing the loud noise.
Jumpier → It is formed from "jump" (from Middle English "jumpe", meaning to leap) and the suffix "-ier" (indicating a comparative form). The word "jumpier" means more prone to jumping or more easily startled than usual.
Think of someone who is more likely to 'leap' or 'startle' — 'jump' means to leap, and '-ier' shows that this person is more so than others.