后缀-ac来源于法语-aque、拉丁语-acus或希腊语-akos,属于形容词或名词后缀，意思是“有...的，患…的，具有…特征或特点的，关于”，有同类后缀：-acal。把后缀-iac也放在这里，是因为这二个后缀有很大的关系，如果您稍微会点英语，请读一下，下面的纯英文关于这个后缀-ac来源，会了解这二个后缀关系及其来源。

英文词源：All words ending in -ac from this source include an i from the original Latin or Greek root, so making it in effect -iac.

Some are adjectives: cardiac (Greek kardia, heart), of the heart; iliac (Latin ilia, entrails), relating to the ilium, a bone in the pelvis, or to the nearby regions of the lower body. Others are nouns: aphrodisiac, a food, drink, or drug that stimulates sexual desire; zodiac, the belt of the heavens that includes the apparent paths of the sun, moon, and principal planets. Some can be both noun and adjective: amnesiac, hypochondriac, insomniac.

Nouns often have linked adjectives in -al (see -al), as in zodiacal and ammoniacal. In a few cases, adjectives in both forms co-exist, as with paradisiac and paradisiacal, or heliac and heliacal (though in both these cases the form in -acal is much more common).

Some words in -ac have related forms in -ic: demoniac and demonic, haemophiliac and haemophilic, maniac and manic. In each of these cases the form in -ic is an adjective, irrespective of the role of the form in -ac. An exception is amnesiac, in which amnesic can be both adjective and noun.

同缀词：

1.maniac [man = mania 疯狂 + -iac(或-i- 中缀 + -ac) 形容后缀 →]
adj.疯狂的,疯狂的人

2.cardiac [card 心，来源于希腊文kardia,同上]
adj. 心脏的

3.heliac [hel 太阳 ,同上]
adj.太阳的

4.coeliac [coel ，同上]
adj.腹腔的,下腹的

5.demoniac [demon 恶魔 ,同上]
adj.恶魔的；凶恶的

6.insominac [in- 不 + som 睡眠 同上 →]
adj. 失眠的;令人失眠的

7.theomaniac [the神 -o-连接字母 ,同上]
n.宗教狂人