The term 'keep in check' is an idiom that means to control or RESTRAIN something. The crossword solutions for this term are REIN (4 letters), CURB (4 letters), LIMIT (5 letters), RESTRAIN (8 letters), REPRESS (7 letters), and CONTAIN (7 letters). All of these words have similar meanings, but each has its own nuances. For example, REIN implies controlling something with a firm hand, while CURB implies controlling something with restrictions. LIMIT suggests setting boundaries, while RESTRAIN implies holding something back. REPRESS implies suppressing something, and CONTAIN implies containing something within certain limits.