Ah, but it can't have been borrowed from Middle Dutch because it was originally found in Old English.
Now I am clueless :s
Heres part of what I found...
Compare Dutch prettig pleasant, nice, agreeable, comfortable (also Belgian Dutch pruttig), German regional (Low German: East Friesland) prettig sportive, funny, humorous, Old Norwegian prettugr tricky, deceitful (compare Old Icelandic prettóttr), also (with metathesis) Middle Dutch pertich cunning, quick, lively (Dutch regional (southern) pertig, Belgian Dutch pertig, also in sense ‘whimsical, capricious’).
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