IPA: /ˈtaɪtli/
KK: /ˈtaɪtli/
In a way that is firm and secure, without any looseness.
She held the rope tightly to prevent it from slipping.
Tightly → It is formed from "tight" (from Old English "tiht", meaning firmly held or secure) and "-ly" (a suffix used to form adverbs). The word "tightly" means in a firm or secure manner.
Think of something being held "firmly" — that's what "tightly" means.