The Latin "sons", to which "sin" is related, means "guilty", but it seems that what is considered sinful - if that and no other disapproving moral term is used - is supposed to be so normally by reference to religious precepts, and indeed it seems better to speak of something as bad or evil if one strongly disapproves of it for moral or ethical reasons without appealing to religious principles or precepts.

Especially in the Christian traditions - both Catholic and Protestant - the notion of sin has been very important, and theologians have spend much mental acuity on its analysis.

The early Fathers of the Church, and the Catholics later, distinguished between relatively minor venial sin and major cardinal sins, a.k.a. as deadly sins.

The deadly sins were those that when not somehow absolved, always with the beneficence and help of the Church, strongly tended to lead to eternal damnation in the hereafter, and to religious persecution, torture or burning in this life.

And in this life, the theological teachings about sin tended to give the Church and its priests and clergy (for the Protestants thought similarly) very great power over their flocks of believers, and must have galled the lifes of many millions, as it also helped persecute and kill many persons whose beliefs or practices were not liked by the worthies of some Christian Church.

Being systematically minded, the early Fathers and later theologians distinguished seven deadly sins in contrast with the seven main virtues.

Here is a table, given both deadly sins and holy virtues, and both the Latin and the English terms:

Seven deadly sins			Seven holy virtues
Latin	English		Latin	English
Superbia	Pride		Humilitas	Modesty
Avaritia	Greed		Liberalitas	Charity
Luxuria	Lust		Castitas	Chastity
Invidia	Envy		Humanitas	Kindness
Gula	Gluttony		Frenum	Temperance
Ira	Wrath		Patientia	Peacefulness
Acedia	Sloth		Industria	Diligence

All of the terms in the table can be explained in various ways, and with more or less plausibility. Indeed all have been explained in quite a few ways, in various Christian sects, and with various justifications, but it is noteworthy that they can not be found, as such, in the Bible, though this has some parallels; that in the above table they are placed, for sins, in the order from worst evil to least evil (amongst the deadly sins); that accordingly, for virtues, the order is from most good to least good; and that the initial letters of the deadly sins, when made into a Latinate term "Saligia", has for many centuries served as a mnemonic.

However they have been explained, it seems that these notions of sin and virtue have been a mostly Christian system of moral dos and donts that gave enormous power and influence to priests and clergy to interfere in the lives of others, in the name of God and with reference to His powers of conferring eternal damnation or infinite bliss.

It is also an interesting fact that the Christian theologians have all held, very humbly of course, that pride is the main deadly sin, which also is an extremely convenient teaching to uphold the power of the churches, and to please the pride and pretensions of their priests and clergy.

In contrast, here is an unbeliever on the subject:

Enjoy and give pleasure, without doing harm to yourself or to anyone else - that, I think, is the whole of morality.
   (Chamfort)

Though possibly too simple as well, this seems a more reasonable and helpful instruction how to live well than the teachings of the churches.

And in any case, it should be remarked about the notion of sin, especially when it is connected with threats with hellfire and eternal burning in the name of an infinitely benevolent omniscient divinity, and most especially when this kind of religious teaching is imposed as true and desirable on small children, who cannot rationally defend themselves, that this seems very immoral to the present writer.