The term 'PREFIX FOR PLASM' can be solved by two crossword solutions: ECTO (4 letters) and PROTO (5 letters). Ecto is a prefix derived from the Greek word ektos, meaning outside. It is used to describe something that is external or outside of a particular system. Proto is a prefix derived from the Greek word protos, meaning first. It is used to describe something that is the earliest form of a particular system. Both ecto and proto are commonly used as prefixes for the word plasm, which refers to a type of matter that is composed of charged particles.