selcouth
Strange, unusual, rare; unfamiliar; marvellous, wondrous.
archaic
'A selcouth novelty,' muttered the knight, 'to advance to storm such a castle without pennon or banner displayed.'
Where it comes from
From Middle English selcouth, from Old English selcūþ, seldcūþ (“unusual, unwonted, little known, unfamiliar, novel, rare”), from seld- (“rarely”) + cūþ (“known”); equivalent to seld + couth.
Adapted from the Wiktionary entry selcouth (CC BY-SA 4.0).