It could be an obsolete word, no longer in use of course. I remember doing an essay on "Felix Randall The Farrier," by Gerard Manley Hopkins, where Felix Randall is described as "hardy handsome." After much struggling with the text, I discovered that "hardy" referred to a tool used by farriers in bygone days. However, I prefer to think that Hogg, was giving a clue to pronunciation in Scots. The vowel sounds in Scots are different from English.