The term 'Wild Blue Yonder' is a phrase used to describe the SKY, particularly the vast expanse of blue that can be seen on a clear day. The crossword solutions for this term are SKY (3 letters) and ETHER (5 letters). SKY is a common term used to refer to the atmosphere surrounding the Earth, while ETHER is an archaic term used to refer to the same concept. Both terms are used to describe the seemingly endless expanse of blue that can be seen in the SKY.