The word 'theodolite' has a mysterious and debated origin. It first appeared in English in the late 16th century, borrowed from New Latin theodelitus. The most plausible theory suggests it is a fanciful, learned construction by an instrument maker, possibly blending the Greek theâsthai ('to view' or 'to behold') with an obscure second element, perhaps the Greek dêlos ('visible' or 'clear'). Despite its Greek-sounding components, the word has no direct ancient lineage and is a modern scientific coinage. Its logic lies in its function: an instrument for making clear and precise observations of angles, a name designed to sound erudite and descriptive for a new technological tool.

The word is a simplex loanword. Its components are not productively separable in modern English spelling. It entered English as a whole unit from New Latin.