The Spanish word 'deriva' (meaning 'drift' or 'derivation') comes from the Spanish verb 'derivar' ('to derive'), which in turn comes from the Latin word 'derivare'. The Latin 'derivare' was formed by combining two elements: the prefix 'de-' meaning 'from, away' and 'rivus' meaning 'stream, river'. So literally, 'derivare' meant 'to draw off water' (like diverting a stream), which later developed the more general meaning of 'to derive' or 'to drift away from a source'.

This etymology makes intuitive sense when you think about how a stream can branch off or 'derive' from a main river, or how something can 'drift' away from its original course - just like water flowing away from its source.

Some related Spanish words include 'derivar' (to derive), 'derivado' (derived, derivative), and 'derivación' (derivation). All these words share the same etymological root and the basic concept of something coming from or branching off from a source.

English speakers might recognize the connection to words like 'derive', 'derivative', and 'derivation'. These words come from the same Latin root 'derivare'. The connection between water flowing away from its source and something being 'derived' from an original source helped shape the meaning of these words in both languages.