in earnest
idiomDefinition of in earnest
1
: in an earnest or serious way
The search began in earnest when the police arrived. After light showers during the day, it began to rain in earnest in the evening. It's hard to tell if he's making this proposal in earnest.
2
: not fooling : serious and sincere
We thought he was joking at first, but then we realized that he was in earnest.