BET - A wager, an agreement between two parties that a stake (usually money) will be paid by the loser to the winner (the winner being the one who correctly forecast the outcome of an event).
BUT - Outside of.
RUB - An act of rubbing.
RUT - Sexual desire or oestrus of cattle, and various other mammals.
TUB - A flat-bottomed vessel, of width similar to or greater than its height, used for storing or packing things, or for washing things in.
RUE - Repentance, regret.
TRUE - Conforming to the actual state of reality or fact; factually correct.
TUBE - Anything that is hollow and cylindrical in shape.
BUTT - The buttocks; used as a euphemism.
BRUTE - Strong, blunt, and spontaneous.
TUBER - A fleshy, thickened underground stem of a plant, usually containing stored starch, as for example a potato or arrowroot.
BUTTE - An isolated hill with steep sides and a flat top.
UTTER - To say.
BUTTER - A soft, fatty foodstuff made by churning the cream of milk (generally cow's milk).