FILL' and OVERFILL (5 letters) The term 'FILL OVERFULL' is composed of two words: 'FILL' (4 letters) and 'OVERFILL' (5 letters). The word 'FILL' means to put something into a space or container, while 'OVERFILL' means to FILL something beyond its capacity. Together, the term 'FILL OVERFULL' can be used to describe the act of filling something beyond its capacity. This could be used in a variety of contexts, such as when packing a suitcase or filling a cup with liquid.