In earnest
Definition 1 of 2

Emphasizing Dedication
Use it to stress the intensity and commitment involved in an action or decision.

He approached his studies in earnest, knowing his future depended on it.
Not Light-Hearted
Suggests a shift from a casual attitude to a more serious one.

After the practice rounds, the competition started in earnest.
Conveys Sincerity
Indicates genuineness, opposite of pretending or joking.

When he apologized in earnest, I knew he meant it.
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