A 14-year-old man, as I learn I should call a Wykehamist, Benjamin Nicholls, has written to me about a suggestion by his 12-year-old sister. She thought that, as the word intelligent means ‘clever’, there should be a word telligent, meaning ‘stupid’.
The sister was aware that the prefix in- signifies negation or privation. She is right in that. Indeed it is related to the Greek a- or an- and the common Teutonic un-, which is where English gets un- from. (In speech the other day I found myself contrasting the pious with people like Samuel Pepys, whom I called unpious, and in the next sentence impious.) Latin, as Mr Nicholls points out, with the example of inimicus, makes free use of this negative prefix, as with utilis, inutilis; nocens, innocens (hence English innocent). Sometimes the prefix is modified by the succeeding consonant to become il-, im-, ir-, or just i- (as in ignarus, ‘ignorant’).
In a light-hearted attempt to cobble up an etymology for a Latin word-form tellego* (the star indicating a form that has not been cited from any source) as the contrary of intellego (later, intelligo), Mr Nicholls even had recourse to the fictional character Telegonus, although he has only one l, and was, as far as I am aware, Greek. He might, perhaps, have tried to derive telligens from the gens, ‘people’, of the tellus, ‘earth’. Sounds stupid enough.
I know that tellus forms the genitive as telluris, but a Latin text from an English source, written in 816 and quoted in the Oxford English Dictionary, similarly misuses tellus: ‘Tamen serventur libros primordiales cum aliis telligraffis’. From this ill-formed Latin word, of which other pre-Conquest examples from Britain are known, an English word, telligraph, was derived, meaning ‘a charter of lands in which the bounds are described’. Nothing to do with telegraph.
But in fact there is no Latin word tellego. Intellego or intelligo bears a modification of the prefix inter-. Intellegere comes from legere, ‘bring together, pick out, catch with the eye, read’, and inter-, ‘between, within’.
Even if it had borne the prefix in-, that in- might have come from the Latin adverb and preposition meaning ‘into, in, within, on, towards, against’, or sometimes having ‘little appreciable force’ in the careful words of the OED – as if the force might somehow be detected under a microscope.
Most of the ordinary English words from intelligere, such as intelligent, intelligence, intellect, came into use by the late 14th century, the days of William of Wykeham.