Definition of "unpin"

unpin

verb
third-person singular simple present unpins, present participle unpinning, simple past and past participle unpinned
1. (transitive) To unfasten by removing a pin.
  Quotations
  Lady Bellaston answered with a smile, “Then you have seen this terrible man, madam; pray, is he so very fine a figure as he is represented? for Etoff entertained me last night almost two hours with him. The wench I believe is in love with him by reputation.” Here the reader will be apt to wonder; but the truth is, that Mrs Etoff, who had the honour to pin and unpin the Lady Bellaston, had received compleat information concerning the said Mr Jones, and had faithfully conveyed the same to her lady last night (or rather that morning) while she was undressing; on which accounts she had been detained in her office above the space of an hour and a half.
  1749, Henry Fielding, The History of Tom Jones, a Foundling
2. (transitive, computing, graphical user interface) To detach (an icon, application, etc.) from the place where it was previously pinned.
3. (programming, transitive) To undo the pinning or fixing of (an array in memory, a security certificate, etc.) so that it can be modified again.
  Quotations
  […] you can use the GCHandle class mentioned earlier to pin a heap block until you explicitly unpin it.
  2012, Ian Griffiths, Programming C# 5.0, page 244
4. (transitive, chess) To get (a piece) out of a pin.