The Spanish word 'costa' (meaning 'coast') comes from the Latin word 'costa', which originally meant 'rib, side, or flank'. The word entered Spanish through Catalan, maintaining the same form 'costa'. This semantic evolution from 'rib/side' to 'coast' makes intuitive sense, as a coastline can be thought of as the 'side' or 'flank' of a land mass where it meets the sea.

Some related Spanish words include 'costilla' (rib), which maintains the original Latin meaning, and 'costado' (side, flank), both of which are derived from the same Latin root 'costa'. These words help demonstrate how the original anatomical meaning of 'rib/side' has been preserved in some derivatives while evolving to mean 'coast' in others.

In English, we have several related words that come from the same Latin root: 'coastal', 'coast', and 'coaster' are direct relatives. The English word 'coast' was borrowed from Old French 'coste', which also came from Latin 'costa'. Interestingly, the English word 'costal' is a medical term meaning 'relating to the ribs', preserving the original Latin meaning.