The term 'prefix for METER' refers to words that can be added to the beginning of the word 'METER' to create a new word. The prefixes ALTI, MILLI, PERI, and DIA all have four or five letters and are commonly used in this context. ALTI means 'HIGH' or 'ABOVE, ' MILLI means 'one thousandth, ' PERI means 'AROUND' or 'surrounding, ' and DIA means 'ACROSS' or 'THROUGH.' Together, these prefixes can be used to create words such as altimeter, millimeter, perimetric, and diathermy.