slather (v.) Look up slather at Dictionary.com
"spread liberally," 1847, of uncertain origin.
Slather on the manure on all the hoed crops, if you have it; if not buy of your improvident neighbor. ["Genesee Farmer," June 1847]
Sometimes said to be from a dialectal noun meaning "large amount" (usually as plural, slathers), but this is first attested 1855; of uncertain origin, it is perhaps from Irish sliotar. Related: Slathered; slathering.