The term 'CASTLE GATE' is a combination of two words, 'CASTLE' and 'GATE'. The first word, 'CASTLE', refers to a large fortified structure, typically built in the Middle Ages by a ruler or nobleman to control a region and protect it from attack. The second word, 'GATE', refers to an entrance or exit point in a wall or fence. The crossword solution for this term is 'PORTCULLIS', which is a type of GATE consisting of a strong, heavy grille that slides up and down in grooves in the walls of a CASTLE. It was used as a defensive measure to prevent attackers from entering the CASTLE.