More (semi-) deep thoughts ;)
Sin covers all wrong doing of any sort.
In many places in the scriptures, iniquity also seems to be a word dealing with all kinds of sin. However, with iniquity, there is a difference. First of all, whereas sin deals with the action or lack of action that is wrong, iniquity deals more with the character or nature of the act.
The word, iniquity, comes from in-equity and it refers to that which is unequal, unfair, or unjust. That explains why David in Psalm 32:5 refers to "the iniquity of my sin." His sinful actions had the character of iniquity of being unequal.
According to "Crabb's Synonyms," iniquity in its more narrow meaning "consists of violating the law of right between man and man."
The Oxford English Dictionary says that it is used especially of "wrongful or injurious actions towards another, infliction of wrong, injury."
To practice iniquity is to be unjust and unequal in our dealings with others. We see this side of iniquity often in scripture. The workers of iniquity are those who eat up God's people like bread (Psalm 14:4), speak peace when mischief is in their hearts (Psalm 28:3), and lay snares for the saints (iniquity an abomination 141:9)
The money Judas received for betraying Jesus is called "the reward of iniquity" (Acts 1:18)
Iniquity is actually the precurser of inequitable actions, rather than just the greedy/proud actions themselves in which iniquity is manifest.
If sin is the result of the natural man, and iniquity the result of the buffetings of Satan, then abominations are also iniquity.