1.  coigne(n = noun.artifact) coign, quoin - expandable metal or wooden wedge used by printers to lock up a form within a chase;
is a kind of wedge

2.  coigne(n = noun.artifact) coign, quoin - the keystone of an arch;
is a kind of headstone, key, keystone

   A quoin. [1913 Webster]
"See you yound coigne of the Capitol? yon corner stone?" [1913 Webster]

   The practice of quartering one's self as landlord on a tenant; a quartering of one's self on anybody. Spenser. [1913 Webster]