Learner's definition of TRUTHFUL
[more truthful; most truthful]
telling the truth
She is a very truthful person. [=she says things that are true; she doesn't lie]
We were not entirely truthful with her about where we went last night.
I like keeping the house clean but, to be truthful, I hate vacuuming.
containing or expressing the truth
He told us truthfully [=honestly] that he had been in the hospital for mental illness.
Truthfully, she deserves most of the credit. [=I am being honest when I say that she deserves most of the credit]