In dead earnest phrase
The phrase is typically used with verbs such as "act", "be" and "speak". The word "dead" can be replaced by "deadly" or can be excluded from the phrase.
If someone does something "in dead earnest", he/she does it with sincerity, seriousness, or determination.
My best friend is in dead earnest about studying abroad next year.
I'm acting in dead earnest to get the promotion.
Martin speaks in dead earnest when it comes to computer science.
From the late 1800s, "dead" means “completely” or “thoroughly” and is used purely for emphasis. [c. a.d. 1000]
very excited and interested
Children are as keen as mustard to discover new things around them.