'unappropriated' originates from Latin, specifically the word 'appropriare', where the prefix 'ad-' (in the Latin root) meant 'to/toward' and 'proprius' meant 'one's own'; the negative prefix 'un-' was later added in English to form 'unappropriated'.

'appropriate' passed into English via Old French 'aproprier' and Medieval Latin 'appropriare'; it became Middle English 'appropriate' and the modern adjective 'appropriated' is the past participle; 'unappropriated' is formed in English by prefixing 'un-' to that past participle.

Initially related to making something one's own ('to appropriate' = 'to make one's own'), the meaning broadened in administrative and financial contexts to 'set aside or allocate (funds)'; 'unappropriated' therefore came to mean 'not so set aside or allocated'.