IPA: /ˈfɪl.ə.bəl/
KK: /ˈfɪləbəl/
Capable of being filled with something.
The form is fillable online, making it easy to complete.
Fillable → It is formed from "fill" (from Old English "fyllan", meaning to make full) and "-able" (meaning capable of). The word "fillable" means capable of being filled.
Think of something that is 'capable of being made full' — 'fill' means to make full, and '-able' indicates the ability to do so.