The term 'stuff to the gills' is an idiom that means to fill something up completely. This phrase can be broken down into five crossword solutions: OVERFEED (8 letters), GLUT (4 letters), GORGE (5 letters), SATE (4 letters), and CRAM (4 letters). OVERFEED means to give too much food, GLUT means to fill to excess, GORGE means to eat greedily or ravenously, SATE means to satisfy fully, and CRAM means to fill tightly. All of these words describe the act of filling something up completely, which is the meaning of the phrase 'stuff to the gills'.