That knacks: in senses of the verb. knacking earnest, downright earnest.
The state or quality of being earnest; (formerly also) †vehemence, great ardour or passion (obsolete).
Earnestness; (also) vehemence, ardour.
The quality of being affectionate (in various uses); †earnestness, eagerness (obsolete); kindly or loving disposition; fondness, kindness.
Seriousness, serious intention.