Decapolis = "ten cities" (see map)
1] a tract of land so called from the ten cities that were in it
   1.a] according to Pliny, these cities were: Damascus, Opoton, Philadelphia, Raphana, Scythopolis, Gadara, Hippondion, Pella, Galasa, and Canatha (Gill)
derivation: from (1176) and (4172)
http://bible.crosswalk.com/Lexicons/Greek/grk.cgi?number=1179&version=kjv

(1176)
1] ten
http://bible.crosswalk.com/Lexicons/Greek/grk.cgi?number=1176&version=kjv

(4172)
1] a city
   1.a] one's native city, the city in which one lives
   1.b] the heavenly Jerusalem
       1.b.1] the abode of the blessed in heaven
       1.b.2] of the visible capital in the heavenly kingdom, to come down to earth after the renovation of the world by fire
       1.c] the inhabitants of a city
derivation: same as (4171), or perhaps from (4183)
http://bible.crosswalk.com/Lexicons/Greek/grk.cgi?number=4172&version=kjv

(4171)
a war a fight, a battle a dispute, strife, quarrel
derivation: from pelomai (to bustle)
http://bible.crosswalk.com/Lexicons/Greek/grk.cgi?number=4171&version=kjv

(4183)
many, much, large,
derivation: including the forms from the alternate pollos
http://bible.crosswalk.com/Lexicons/Greek/grk.cgi?number=4183&version=kjv

Comment:
The names of the Ten Cities as shown on the map (from north to south) are Damascus, Canatha, Dion, Hippus, Raphana, Gadara, Scythopolis, Pella, Gerasa, and Philadelphia. The names on the list of Pliny (as quoted by Gill) are Damascus, Opoton, Philadelphia, Raphana, Scythopolis, Gadara, Hippondion, Pella, Galasa, and Canatha. Eliminating those which are the same on both lists leaves Dion, Hippus, and Gerasa on the map list, and Opoton, Hippondion, and Galasa on Pliny's list. If Hippus and Hippondion are assumed to be the same, and  Galasa and Gerasa are assumed to be the same, and are therefore eliminated from the lists, only Dion and Opoton remain. The tentative conclusion is therefore that Dion and Opoton are two names for the same city. Unfortunately, a map which shows the location of Opoton was not found. A document which says that Dion and Opoton are two names for the same city was also not found. So it remains short of certain that Dion and Opoton are one and the same city.

A link to each occurrence of this word in the homepage:
1] Decapolis