Birdy, it's not only in the US that
bolded is being used in this way. I tried the word myself in the puzzle, but unlike you I wasn't surprised it was rejected, since I know a lot of recent usage trends are not yet reflected in our word list.
(Come to think of it, most of the forumites suggesting words are surprised / astonished / thunderstruck / totally bewildered that their words are not accepted.)
The Shorter Oxford has an obsolete sense of
bold as a verb, meaning to embolden, to appear bold, etc. An example of this usage is in the 16th century translation of Apuleius's
Golden Ass, by William Adlington:
Then she tooke me by the halter and cast me downe upon the bed, which was nothing strange unto me, considering that she was so beautifull a Matron and I so wel bolded out with wine...
I'll draw a curtain of modesty over the rest of that scene.
The sense of the word that you (and I) had in mind is covered by the Canadian Oxford, which has
bold as a transitive verb meaning "set or present in bold type". Wiktionary has this meaning too, but the other dictionaries I looked at haven't caught up with it yet.
I
will add this word to our list.
