The term 'ARM EXTENSION' can be broken down into two crossword solutions, FUL and ORY. FUL is an abbreviation for the word 'FULLY', which means completely or entirely. ORY is an abbreviation for the word 'ORIENTATION', which is the process of adjusting or aligning something to a particular position or direction. Therefore, ARM EXTENSION can be summarized as the process of completely or entirely adjusting or aligning the ARM to a particular position or direction.