What is definition of this proverb or saying:
Ein Fund verholen ist so gut wie gestohlen.
Is it common nowadays? Under which circumstances we use it?
The version that I have found (XVI) is
Ein Fund verhohlen, ist so gut als gestohlen.
Using wie instead of als fits modern grammar, and I also have found a variant with einen Fund, which can be seen as more correct (Akkusativ, Maskulinum).
What this expresses is that keeping secret something which one has found is equivalent to theft.
Fund is something that has been found. The word verhohlen is derived from verhehlen as its past participle. The modern past participle is verhehlt, but it seems to be necessary to me to see verhohlen as a past participle here to make sense of the sentence.
The meaning of verhehlen is to hide, to keep secret. I think that it is not in common use today except referring to not saying something out loud, and then mostly negated: Ich will nicht verhehlen, dass ich das Wort in diesem Zusammenhang anfänglich nicht erkannt habe.
I had not heard the saying before, but I cannot say whether it is still in common use somewhere.