I read this on Chabad.org in its discussion of Parshat Vayikra:
• The different types of “sin offering” (chatat) brought to atone for transgressions committed erroneously by the high priest, the entire community, the king or the ordinary Jew;
• The “guilt offering” (asham) brought by one who has misappropriated property of the Sanctuary, who is in doubt as to whether he transgressed a divine prohibition, or who has committed a “betrayal against G‑d” by swearing falsely to defraud a fellow man.
It seems that the asham, or guilt offering, applies to a lesser category of sins than the sin offering, chatat. For example, asham is used when there is merely a suspicion that a sin has been committed. However, it is odd to me to find the sin of slander, which is generally considered a fundamental Jewish transgression--and, along with stealing, a breach of the Ten Commandments--listed among these "second-class" sins.
What are some interpretations for why this is so?