The word "xenolith" comes from two Greek words" xenos (ξ𝜉𝜈𝜊𝜍), meaning "foreign" or "strange", and lithos (λίθος) meaning "stone".  Therefore, xenolith literally translates to "foreign stone" or "foreign rock". This name accurately describes the geological term for a rock fragment that is foreign to the igneous rock in which it is embedded. 

According to the Oxford English Dictionary (OED), the word "xenolith" was first used in English in 1894 by the geologist and anthropologist William Sollas.  This aligns with information from other dictionaries, such as Merriam Webster, which also notes its first known use in 1894. 

Examples of "xenolith" used in a sentence: 
"The geologist found a xenolith of granite within the basalt, a fragment from a deeper layer of the Earth's crust." 
"The volcanic ash contained chunks of xenoliths, which were pieces of mantle and crust from the eruption."   
"However, rare xenoliths of sedimentary rocks occur in the granite." 
"The parental magma for pyroxenite xenoliths could be derived from the partial melting of the asthenosphere with continental crust material involvement and of the upper lithospheric mantle." 

All I can say is "wow" and "thanks". Today's word word of the day has extended my knowledge. 

Just the facts:

XENOLITH Definition & Meaning - Merriam-Webster

16 hours ago, Paladin said:

All I can say is "wow" and "thanks". Today's word word of the day has extended my knowledge. 

I agree.  Thanks, @Myr.