The syllables of the spells all have some meaning, showing how the spells work. Though generally all spells have an element in them, other parts have the meaning otherwise. Here is a list I've compiled that has a lot of meanings based on syllables that have appeared in more than one demon's spells, to make sure they're more accurate. I also put in the katakana for some of them.

General Rules:
Words before spells are upgrades or different versions of the attack.
Similar sounding first words have similar effects. E.g. Ganzu, Ganjasu
Some demons have spells with endings no other demons have, Wonlei has -ren. Riou has -fanon
Some demons share spells. e.g. Kid and Koruru have Zerusen.
Syllables of spells places at the beginning of spells sometimes have different meanings from when they
Though longer spells are usually stronger, some are just variations, and the strongest spells are the ones
with the strong base word like "Gigano" "Dioga" "Shin" and "Baou".

Prefixes/Secondary Words:
Ma Attack varies on heart of the user lv2 マ
Ra Reflecting ラ
Gigano/Giga/Giru (variations) upgrade lv2 ギガノ
Giga Ra Reflecting shield ギガラ
Dioga extreamly powerful blast lv3 ディオガ
Baou (first letter(s) variations) Similar to Dioga, animal spell lv3 バオウ
Raajia Huge version ラージア
Ganzu Rapid fire (often machine gun) attack lv2 ガンズ
Gou Increased destructive power ゴウ
Jauro (variations) Flower-shaped attack ジャウロ
Forusu Fourth Level lv3 フォルス
Aagasu Monster shield spell, protects caster from all sides with giant teeth アーガス
Sorudo Sword spell ソルド
Shizeruku Scissor spell シザルク
Barudo Stronger spell, usually hits a larger area lv3 バルド
Riou Double attack リオル
Giru- Stronger attack, similar to gigano.
Oru- Long attack using whips (Movement controlled by demon) オルダ
Amu- Punch attack アム
Garu Spinning/drill shaped attack ガル
Ko- Small form attack コ
Teo- Upgrade, usually larger and stronger form of a basic spell テオ
Ze- "Normal" attack (Beam, physical attack)
Ra Reflecting ラ
Bi- long distance attack
Rondo- Whip attack ロンド
Reedo- Spinning blade attack
Doru- spike or drill related/shaped attack ドル
Seu- Dome/shphere shaped spell
Shin Similar to Baou, highest ranking in power
Bo-i- Dome shaped attack or shield
Supu- Opponent's spell destroying attack.

Suffixes:
-ru basic elemental attack lv1 ル
-su variation of attack/elemental attack lv1 ス
-mu attack of high energy lv1 ム
-ga basic ugrade lv2 ガ
-don upgrade of -su attacks and not elemental attacks lv2 ドン
-shiru shield シルド
-garu elemental blast
-ku spell relating to the body ルク
-sen shoot セン
-do conditional spell, doesn't directly do damage to opponent ド
-ron operating attack ロン
-gu energy manipulation グ
-yoyo yo-yo like attack ヨーヨー
-eido shoots substance or soft object, usually from mouth or head. レイド
-an attack used to or involves cutting, crushing, breaking (of ground, wood, rock) *ン
-io special effect attack ィオ
-dio similar to dioga, more monstrous form ディオ
-gu attack involving manipulating energy long distances グ
-buruku Multiple-body spell ブルク
-un wall-like attack ュン
-rei energy discharge in a specific direction レイ
-fei flight spell フェイ
-jio having to do with the demon's physical and mental state (scary, healthy, slow) ジオ
-zu multiple parted attack ズ
-roro multiple scythe like attack ロロ
-jasu underground attack ジャス
-tsu multiple small sharp attacks ツ
-boru giant darkness spell
-kurei curling "clay-like" spell
-noon/on/no Long rope like attack, stronger than ron. Attack at tip.

That's my personal observation, though this is a major part of speculation in japanese. Here is a site that lists everything in more detail. (Though it's in japanese)

http://ja.wikipedia.org/wiki/%E9%87%91%E8%89%B2%E3%81%AE%E3%82%AC%E3%83%83%E3%82%B7%E3%83%A5!!%E3%81%AE%E5%91%AA%E6%96%87%E4%BD%93%E7%B3%BB