Dana: Da = "Do-a, father a; na = knot, bond. Give, anti-up, pay ya dues; deal it out; divvy up; Given (in marriage, as a presumption); to dedication to, bound to, bound in (vows, marriage).
Kappa = "fitting" as in the hardware used on boats or the gear used with horses; from that to "it fits" (it works); to it works properly; to it's fitting or proper.
Giving is seen as a service done by the receiver to the giver because of an understanding of kamma. Kamma is the doing of an intentional act and it's consequences, which is approximately the golden rule except that the rebound is not one for one, but is greatly magnified, and included as deeds are acts of mind and speech.
In the Buddha's system giving is not considered an essential part of escape from Dukkha because it involves making kamma where the escape from Dukkha is equivalent to the escape from kamma. However Buddhists are always advised to develop a generous attitude and retain it throughout life. For the beginner generosity is advisable to create a "store" of good kamma because knowing one has some good stuff coming calms the mind and a calm mind is essential for seeing things as they are. The more advanced practitioner is generous as a good example to others.
Acceptance in the Old Days was by silence. No waste words. If there was a reason for non-acceptance, that was voiced.

Further Resources:
The Method: Dana