affixes and roots for underling and droplet

In Droplet, -let is a suffix (from French, maybe?) that means small. Other words that use this suffix are Leaf and Twig.

I'm not sure how underling works. It may have been created as a whole, rather than a combination of noun and suffix. "Under" is sometimes used as a prefix, as in undersecretary, but you can't speak of "an under" nor of "a ling" so I'm not sure how they got together.

Roberta?

American heritage dictionary has a listing for -ling, with a dash, leading me to believe ling is a suffix as well. (meaning: diminutive). Also under has a dash (under-) after the word, probably indicating it is a prefix.

Questions:

1. listings with dashes before and after, are these prefixes and suffixes?
2. if under is a prefix and ling is a suffix, where is the root of the word?

thanks again.