In many years as a native English speaker, I’ve never met the word “planish” until I saw it in the discussion at Siehe auch: eingeebnet
where it was suggested for translating eingeebnet.
Looking at the Leo entry for planish, I see that only once is it shown as technical.
Looking at the Leo entry for einebnen, I see that there is no indication that planish isn’t an equivalent to einebnen, but is only used in a limited technical context.
I suggest that any mention of planish be accompanied by the indication that it is a verb with a restricted use, to avoid the risk that that people are misled into using planish as an ordinary everyday English word.
I don’t think planish is a word in common use – or am I wrong?