eager
A seven-letter word meaning serious and eager could be "earnest".
That could be zeal or zest.
Zeal
A four letter word meaning not kosher is: tref
Eager
keen
Agog
anxious, enthusiastic, interested, alert, and eager
eager
enthusiastic, passionate, eager, spirited, keen, fired, devoted, dedicated
keen
· kitchen - place to cook the turkey · knife to cut the turkey
OK THEN THAT IS REALLY SINCERITY
Restlessly eager might be antsy.
It is keen
A seven-letter word meaning serious and eager could be "earnest".