No, an omnibus is a large book covering several subjects or topics.
wavy
Your thickly fat.
It means to spread or apply thickly as you would jelly on toast.
Justice for all.
Yes, thickly is indeed an adverb.Some example sentences are:She lives in a thickly populated area.The thickly-clothed man makes his way through the ruins.
the plains are thickly populated
It is a Latin word meaning everyone or everything. The first examples of public transport were called "omnibus vehicles" because they carried everyone. Eventually that got shortened to "omnibus" and finally to "bus".
The sun shines for all
If by "least inhabited" you mean human habitation, it must be Antarctica.
Thickly snouted pipefish was created in 1814.
Quisque pro omnibus means "each for all".
I love hot toast, thickly spread with best butter.