A girl with a very sexy body but an unattractive face... This phrase is generally uttered by men who examine the posterior of a lady as they drive by, On the approach they say "Oooohhh" and if her face does not match the beauty of her posterior as they pass they will say "Naaaaaa", hence Una.
A typically Northern Irish expression also spoken as "face as long as a Lurgan spade" meaning to look miserable or long faced.
One theory about the origin of this expression is that a “Lurgan spade” was an under-paid workman digging what is now the Lurgan Park lake. Another theory is that it is a translation from the Irish language lorga spád meaning the shaft/shin of a spade.
Upon observation you would say...