The word "dappled" likely originated from Scandinavian roots, specifically from Old Norse "depill" meaning "spot." 

According to the Oxford English Dictionary, the adjective "dappled"  was first used in English around the year 1400, during the Middle English period (1150-1500).  It appears in Mandeville's Travels.  It entered Middle English as a word referring to markings on an apple or a gray horse with spots resembling apples. 

According to the Oxford English Dictionary, the noun "dapple" probably came to English from the word dappled before 1586, in the writings of Sir Philip Sidney.  Dapple as a noun meant a patch or spot of color or light.  Dapple an adjective is also recorded as an adjective from the mid 1500s. OED's earliest evidence for the adjective form is from 1551, found in the writings of Thomas Wilson.  The earliest known use of the verb "dapple" is in the early 1600s. OED's earliest evidence for the verb form is from 1600, in the writing of William Shakespeare.   The verb "dapple" meant mark with spots or rounded patches.

Examples of the word "dappled" used in a sentence:  
"Her hair had come loose from its braid and red marks dappled her chest." 
"In a few moments both were sleeping in the dappled shade."  
"Sometimes I carry a book out under the pear trees and sit in the dappled shade."  
"The path was dappled with sunlight."  
"The horse under him was dappled grey."