'reallocate' originates from Latin elements: the prefix 're-' (from Latin 're-') meaning 'again' or 'back', combined with 'allocate' which comes from Latin 'allocare'.

'allocate' comes from Latin 'allocare' (to place, assign), passed into Old French as 'alouer/alloer' and into English as 'allocate'; the modern English verb 'reallocate' formed by adding the prefix 're-' to 'allocate'.

Initially related to 'place' or 'assign' (from Latin 'allocare'); with the prefix 're-' it developed the specific sense 'to assign again or differently', which is the current meaning.