'unannexable' originates from English prefix 'un-' (a negative prefix) + 'annexable', where 'annex' ultimately comes from Latin 'annexare' (from 'ad-' meaning 'to/toward' + 'nectere' meaning 'to bind').

'annex' passed from Latin 'annexare' into Old French as 'annexer' and into Middle English as 'annex'; the adjective 'annexable' was formed with the suffix '-able' and later the negative prefix 'un-' produced 'unannexable'.

Initially related to 'binding or fastening to' (Latin sense), it evolved to mean 'to incorporate (territory) into a political entity'; 'unannexable' therefore denotes something that cannot be incorporated or annexed.