The Spanish verb 'sellar' (to seal) traces its origins back to Latin. It comes from the Latin verb 'sigillare' meaning 'to seal', which was derived from 'sigillum' meaning 'seal' or 'small mark'. Going even further back, 'sigillum' was a diminutive form of the Latin word 'signum', meaning 'mark' or 'sign'. The evolution from 'sigillare' to 'sellar' involved the common sound change where Latin 'gi' became Spanish 'll', and the unstressed 'i' was dropped.

Some related Spanish words include 'señal' (signal, sign) and 'seña' (sign, gesture), which also derive from Latin 'signum'. The connection between sealing something and making a mark or sign is clear - when you seal something, you're typically marking it in some way to show it's official or complete.

English speakers might recognize the connection to words like 'sign', 'signal', and 'signature', which all come from the same Latin root 'signum'. Even the English word 'seal' itself, though it comes through a different path (via Old French), ultimately relates to the same Latin word 'sigillum'. This shows how the concepts of marking, signing, and sealing have been closely related throughout the history of these languages.