If a weather forecaster were to predict a period of siccity, his audience would be unlikely to understand that he meant a drought was on its way. This ancient word for a state of extreme dryness has long ago been abandoned by English speakers.
That might be because it’s odd-looking, so that people have preferred the native English dryness. A century ago, it was already marked as “probably obsolete” in the first edition of the Oxford English Dictionary. But it has never been popular. Eighteenth-century chemists might have referred to evaporating a liquid to siccity, to dryness, geographers might have described an area as characterised by extreme siccity when they meant that it was a desert, learned men might make a little joke on the siccity of a sermon, but otherwise it had small use and limited circulation. When this item appeared in Scotland a century and a half ago it must even then have seemed curiously old-fashioned and obscure:
The siccity of the weather is already so marked that a scarcity of water is beginning to be felt.
The Dundee Courier & Argus, 27 May 1865.
Siccity comes from Latin siccus, dry. A browse through the OED shows that we’ve lost more than one word from this source. Who now speaks or writes of something being siccaneous, or of siccating something, that is, making it dry? In a specialist arena, the noun siccative remains in use for a substance that’s added to a liquid such as paint to promote its drying. However, we do retain desiccate and its relatives from the same source.
By the way, the mainly American verb sic, to attack or provoke into attacking (“He sicced his dog on them”) is quite separate in origin, being a variation on seek. And sic, which marks some text quoted exactly as it stands in the original, is the Latin word “thus”.