Six-gun and Side arm

Six-gun noun - A pistol with a revolving cylinder (usually having six chambers for bullets).

Side arm and six-gun are semantically related. In some cases you can use "Side arm" instead a noun phrase "Six-gun".

Side arm noun - A firearm that is held and fired with one hand.

Six-gun and side arm are semantically related. Sometimes you can replace phrase "Six-gun" with "Side arm", this phrases are similar.