'endorsable' originates from the English verb 'endorse' with the adjective-forming suffix '-able', where '-able' meant 'capable of'. 'Endorse' in modern English ultimately comes from Old French 'endosser' (to put on the back), built from 'en-' + 'dos' (back).

'endorse' changed from Old French 'endosser' and Medieval Latin 'indorsare' (literally 'to put on the back') and eventually became the modern English verb 'endorse', from which the adjective 'endorsable' is formed.

Initially the verb meant 'to write on the back (of a document)' and later developed the sense 'to sign, approve, or publicly support'; consequently 'endorsable' now means 'able to be endorsed' in both the literal (can be signed) and figurative (can be supported) senses.