The term 'MAKE A SIBILANT SOUND' can be solved by two crossword solutions: SISS (4 letters) and WHISH (5 letters). A sibilant sound is a type of consonant sound that is produced by forcing air through a narrow channel in the mouth, resulting in a hissing or whistling sound. Examples of sibilant sounds include the 's' sound in 'SUN' and the 'sh' sound in 'SHIP'. To make a sibilant sound, one must form their mouth into a narrow channel and force air through it.