in earnest

[in earnest] {adv.} or {adj. phr.} Seriously; in a determined way.

The beaver was building his dam in earnest.

Bill did hishomework in earnest.

- Often used like a predicate adjective.Sometimes used with "dead", for emphasis.

Betty's friends thoughtshe was joking when she said she wanted to be a doctor, but she was indead earnest.