Euphemisms are basically polite ways of saying impolite things. They are generally characterized by verbal ambiguity and are often idiomatic. For example, instead of saying that someone has died, one might say that he/she has “passed away” or he/she has “gone on to be with the Lord.”
In a recent article Freddy Boswell, “Are You Sure You Can Say That?! Fresh Considerations in Translating Euphemisms” Bible Translator 60 (2009):132–9, notes that there are four main categories of euphemisms in the Bible.
(1) Euphemisms related to certain body parts or body functions (e.g., I Sam 24:3; Gen 18:11; Luke 1:59; 8:43).
(2) Euphemisms related to sexual activity (e.g., Gen 4:1).
(3) Euphemisms related to death (e.g., Gen 49:29; Josh 23:14; 1 Thess 4:13).
(4) Euphemisms related to the divine name Yahweh (e.g., Matthew’s preference for Kingdom of Heaven as opposed to Kingdom of God).