Fun:Four Letter Words

Four Letter Words in English are those that, due to their referents and easy pronouncability, are shunned by prudes, prigs and politicians (in public).

A short list will make it obvious to the reader why these words are usually considered taboo:
 * 1) Host
 * 2) Once
 * 3) Trap
 * 4) Acne
 * 5) Note
 * 6) Dash
 * 7) Work
 * 8) Easy
 * 9) Trip
 * 10) Bork
 * 11) Undo
 * 12) Tick
 * 13) Tock
 * 14) Suck
 * 15) Earn
 * 16) Xenu
 * 17) Rope
 * 18) Ouch
 * 19) Cusp
 * 20) Kite
 * 21) Skit

It should be noted that "four" and "word" are four letter words, as is "goat".

As a point of curiosity, there are 456.976 possible combinations of four letters, so even excluding the impossible ones gives a lot of room for play.