The term 'sheepish sound' can be described by three words with 3, 4, and 5 letters respectively: BAA, MAA, and BLAT. BAA is a sound made by sheep, which is similar to the sound of a goat, and is often used to describe a timid or embarrassed person. MAA is another sound made by sheep, which is a softer version of BAA. Lastly, BLAT is a sound made by sheep that is similar to a BLEAT, which is a high-pitched sound made by sheep and goats.