Other forms: liaising; liaises
When you liaise with someone, you meet up or connect with them, usually so you can work together on something cooperatively. Two rival soccer teams might liaise to discuss the muddy conditions of the town's soccer fields.
The verb liaise comes from the noun liaison, which was adapted from its original French meaning ("a binding together") during World War I to mean "military cooperation or alliance" between different countries. The Latin root of both words is ligatio, "a binding." When two groups liaise, they bind together or connect in order to gain a result that they both want. The very trickiest thing about the word liaise is remembering that it's spelled not with one i but with two.