The Spanish word 'rellena' comes from the verb 'rellenar' meaning 'to fill again' or 'to refill'. This verb was formed by combining three elements: the prefix 're-' (meaning 'again'), the adjective 'lleno' (meaning 'full'), and the verb suffix '-ar'. The word 'lleno' itself comes from Latin 'plenus' meaning 'full'. The transformation from Latin 'plenus' to Spanish 'lleno' shows a common sound change where the initial 'pl-' cluster in Latin became 'll-' in Spanish.

A simpler and very common related Spanish word is 'lleno' meaning 'full'. This is a fundamental Spanish adjective that you'll encounter frequently. For example, 'El vaso está lleno' means 'The glass is full'. Understanding this connection helps remember that 'rellena' essentially means 'filled again' or 'refilled'.

The Latin root 'plenus' that gave us Spanish 'rellena' also gave English several words. You might recognize it in words like 'plenty' (having a full amount), 'plenary' (fully attended), and 'replenish' (to fill again). Notice how 'replenish' carries the same 're-' prefix and similar meaning as Spanish 'rellenar'!