The Spanish preposition 'tras' meaning 'after' or 'behind' comes from the Latin word 'trans' meaning 'across' or 'beyond'. The evolution from Latin to Spanish involved both phonetic simplification (dropping the final 'n') and a slight shift in meaning. While the Latin 'trans' emphasized movement across or beyond something, the Spanish 'tras' developed to focus more on the sequential or spatial relationship of following or being behind something.

Several common Spanish words contain this same root, including 'trasero' (rear, back), 'traspasar' (to pass through, transfer), and 'trasladar' (to move, transfer). All these words maintain the core idea of movement or position relative to something else.

Many English words contain the Latin root 'trans-', making them cousins of the Spanish 'tras'. Common examples include 'transfer', 'transport', 'translate', and 'transition'. All these words involve the idea of movement across or beyond something, preserving the original Latin meaning. The English prefix 'trans-' maintained the original Latin form and meaning more closely than Spanish 'tras'.