Family Name:
石 (ishi) = stone, rock, pebble
田 (da) = rice field
Given Name:
竜 (ryuu) = dragon
弦 (ken) = string, bowstring

The characters for Ryuuken's name are fitting. Dragons ('ryuu') are symbols of the emperor; they represent both imperial sovereignty and spiritual power. The 'ken' is a reference to the Quincy use of bow and arrows as the weapon of choice to fight Hollows. His name is very suggestive of his status as patriarch of the Ishida family, his power, and his distance.

'Ishida' is probably a fairly normal family name; the 'da' (or 'ta') is common in Japanese surnames. It seems very dismal, though. Who wants a rice patty and rocks in the same name?

It is more obvious when seen in actual Japanese, but the 'ken' (弦) in Ryuuken's name is the same character used to write 'Souken' (宗弦). Similarly, the 'ryuu' (竜) in his name is the same 'ryuu' in Uryuu (雨竜). Traditionally, a child is given a character from his or her parent or grandparent's name as a sign of honor.