The term 'strong unpleasant smell' can be described using four different words: STINK (5 letters), STENCH (6 letters), REEK (4 letters) and PONG (4 letters). STINK is a verb meaning to emit an unpleasant odor, while STENCH is a noun referring to a strong, foul smell. REEK is also a verb meaning to emit a strong, unpleasant smell, while PONG is a noun referring to an unpleasant smell. All four words are used to describe a strong, unpleasant smell that is often associated with something rotting or decaying.