stock-still

"stock" は沢山の意味があるのでこれまでにも4回も取り上げています。（下記参照）　Reader's Digest 8月号の旅行記事 The SPIRIT of DUBLIN の次ぎの個所に出てきた "stock" は過去に取り上げた "stock" とも意味が違っています。
One man on a bar stool, who looked like the grizzled singer Joe Cocker, suddenly launched into a ballad about a sailor at a Spanish port where woman with "dark eyes and dark hair" will "give you some more" even when "all your money is spent". I watched the intent faces on the two fiddlers: they sat stock-still except for their arms and hands.
早速 "stock-still" を辞書で調べます。
・Collins Dictionary: absolutely still; motionless: Bethan was sitting stock-still on a sofa with Isabel beside her, holding her hand.
・Cambridge English Dictionary: without moving; completely still: On seeing us, the deer stood stock-still for a moment, then turned and retreated into the forest.
辞書で "stock" を見ても、どの意味がこの "stock-still" になるのか分かりませんでしたが、Online
Etymologyに:
Stock-still (late 15c.) is lit. "as still as a tree trunk." の説明がありました。
参照
"stock character": http://blog.alc.co.jp/blog/3302827/archive/2007/2/20
"stock": http://blog.alc.co.jp/blog/3302827/archive/2007/4/1
"lock, stock and barrel": http://blog.alc.co.jp/blog/3302827/archive/2009/8/24
"take stock": http://blog.alc.co.jp/blog/3302827/archive/2011/3/15