The difference between Extremely and Terribly

When used as adverbs, extremely means to an extreme degree, whereas terribly means so as to cause terror or awe.

check bellow for the other definitions of Extremely and Terribly

Terribly as an adverb (literary, _, or, _, dated):

So as to cause terror or awe.

Examples:

"The lion roared terribly."
Terribly as an adverb:

Very; extremely.

Examples:

"He's terribly busy and you really shouldn't bother him."
Terribly as an adverb:

Very badly.

Examples:

"She took part in the karaoke, but sang terribly."