'moorable' is formed in modern English by adding the productive suffix '-able' to the verb 'moor', where 'moor' means 'to make fast (a vessel)' and '-able' means 'capable of or suitable for'.

The verb 'moor' has been used in English since Middle English (from forms like 'moren'), describing securing a vessel; the adjective 'moorable' is a later, regular formation using the suffix '-able' to mean 'capable of being moored'.

Originally the root verb meant 'to secure a vessel'; over time the derived adjective came to mean 'capable of being secured' or 'suitable for mooring', a straightforward extension of the original action.