In the phrase it most famously appears in (and as in uffish thought he stood) it appears to be an adjective. Carroll explains it as "a state of mind in which the voice is gruffish, the manner roughish, and the temper huffish," which suggests that it means something along the lines of "grumpy" ... which is usually an adjective itself (it can also be capitalized and used as a proper noun, as can Happy, Sleepy, Sneezy, and Dopey).