This ROOT-WORD is the Prefix SUB which means UNDER & BENEATH. This is a very useful ROOT with history both ancient and modern right down to our own SUBway. Please note the difference in accent of No. 7 and No. 8. They are the same word, but one is a noun the other a verb. Notice also the change in spelling of Nos. 9 and 10. The Latin verb mergere, to plunge, becomes mersus in the past participle. SUBurban comes from urbs, city. In ancient Rome the city was built on the hill for a position of safety. Outlying districts were below.