'terrestrial' originates from Latin, specifically the word 'terrestris,' where 'terra' meant 'earth.' 'Focus' originates from Latin, specifically the word 'focus,' meaning 'hearth' or 'fireplace.'

'terrestris' transformed into the Old French word 'terrestre,' and eventually became the modern English word 'terrestrial.' 'Focus' remained largely unchanged from Latin to modern English.

Initially, 'terrestrial' meant 'of the earth,' and 'focus' meant 'hearth.' Over time, 'focus' evolved to mean 'center of activity or interest.'