The term HIGH PART refers to the highest part of a musical composition, often sung by a soloist. The crossword solutions for this term are UPPER (5 letters), TREBLE (6 letters), and FALSETTO (8 letters). UPPER is a term used to describe the highest register of a voice or instrument, while TREBLE is a term used to describe the highest range of notes in a musical composition. FALSETTO is a vocal technique used to produce a higher pitch than the singer's normal range.