Transgression, n.
Etymology: [L. transgressio a going across, going over, transgression of the law, from transgredi, transgressus, to step across, go over; trans over, across + gradi to step, walk: cf. F. transgression. See Grade.]
The act of transgressing, or of passing over or beyond any law, civil or moral; the violation of a law or known principle of rectitude; breach of command; fault; offense; crime; sin. Forgive thy people . . . all their transgressions wherein they have transgressed against thee. I Kings viii. 50. What rests, but that the mortal sentence pass On his transgression, death denounced that day Milton. The transgression is in the stealer. Shak.
Syn. -- Fault; offense; crime; infringement; misdemeanor; misdeed; affront; sin.
Shades of meaning
Fernald has no entry of its own for transgression; he lists it under sin.
Where he writes about it:
Transgression, as its etymology indicates, is the stepping over a specific enactment, whether of God or man, ordinarily by overt act, but in the broadest sense, in volition or desire. — from sin
Sin may be either act or state; transgression is always an act, mental or physical. — from sin
Sin in the generic sense, as denoting a state of heart, is synonymous with depravity; in the specific sense, as in the expression a sin, the term may be synonymous with transgression, crime, offense, misdeed, etc., or may denote some moral activity that could not be characterized by terms so positive. — from sin
Sin is thus the broadest word, and immorality next in scope; all crimes, properly so called, and all immoralities, are sins; but there may be sin, as ingratitude, which is neither crime, transgression, nor immorality; and there may be immorality which is not crime, as falsehood. — from sin