With a consideration of the local lateral freedom of molecules, a general equation of state for columnar liquid crystals is derived, which is in agreement with the one obtained by Wensink [1] in the density limit. It is also shown that air additional negative pressure, which is not negligible, tends to be generated for thick disc-like liquid-crystalline molecules even in, a high-density regime because of the cavities they create as a result of the allowed lateral motion.