Package glossaries - single spaced \printglossaries?

Solution: use

\renewcommand*{\glsgroupskip}{}

Explanation: Abbreviations are bunched according to the starting letter. In your example, you can see this additional spacing is between the A-list & B-list and the B-list & C-list. This is the normal behavior of the glossaries package and is useful whenever the glossaries run to several pages. For smaller glossaries, it doesn't make a lot of sense.

Given the default glossary entry "style" isn't what you want, why not select another one via the \printglossary style options (e.g., \printglossary[style=altlist])? The manual sets out quite a few styles that might work for you.

Out of these, I expect that \printglossary[style=long] will work best. However, since this style relies on the longtable package, you'll need to be sure that glossary can access it.

Also, you might notice that the style=long option doesn't set glossary entry names in bold font as before. If you still want that, just add \renewcommand{\glsnamefont}[1]{\textbf{#1}} to your document preamble to get it back again.

I solved this with \glsnogroupskiptrue before of \printglossary. I was using a custom style based in long style and for some reason remained the spacing skip between groups and \renewcommand*{\glsgroupskip}{} do not worked at all.

Oddly, it seem that only \glsnogroupskipfalse appear in the manual (page 8) . It should be evident that this is a boolean option that must have a opposite command, but it would have been better see it written.