(Darren) "Enlarge" is from the French enlarger and may just be a copy, so to speak. A more regular formation, reading between the lines of my 1964 COD, would be "largen", (cf thicken) the prefix en- + adjective being rare. En- + noun or verb is common though and explains "enliven" either as "to give life to" or to (intensively) liven.

[Rosie] ...which has both prefix and suffix. As does embolden. But you can't ensticken the affixes on ad lib.

You people scare me a bit sometimes. I love you all, but you scare me mildly.

(Raak) With "embolden" and "enliven" it would seem that in the past someone has done just that. I don't think the rules are particularly well-defined. (nights) Yep, we're a bunch of swivel-eyed fundamentalists. In the beginning was the Word. AND THE WORD SHALL BE SPELT PROPERLY. :-)