English
slatestone
From slate + stone.
Proto-Germanic *slaitijaną
Frankish *slaitijan ‘to split, break’
Old French esclater ‘to break, shatter’
Old French esclate
Middle English sclate
English slate
Proto-Indo-European *steyh₂- ‘to stiffen’
…
Proto-Germanic *stainaz
Proto-West Germanic *stain
Old English stān
Middle English ston ‘a stone’
English stone
Today it means
noun slate
Language periods are conventional ranges, not dates for this word.
Etymograph / slatestone