Q From Turner Hooch: Why is there a letter n at the end of the word column?
A Or, putting it another way, why it is there but not pronounced?
The source of our word is the Latin columna, which had a syllable break between the m and n, so both letters were pronounced. It appeared in English like that in the fifteenth century, but it was a rather unEnglish looking (and sounding) word, and it went through a lot of changes and different spellings in the following 250 years.
The most characteristic change was to drop the ending altogether, so leaving a word with roughly the same pronunciation as we use now, but spelled colum. However, the spelling varied a lot at this period: others added a b to make it colomb; some kept the last syllable of the Latin word, but respelled it as columne.
The spelling seems to have settled down to our modern form from the latter part of the seventeenth century onwards; an early example is in John Milton’s Samson Agonistes of 1671: “As in a fiery column charioting His godlike presence”. One of the last examples of the old forms appears in the diary of the antiquarian Thomas Hearne for 1712: “The Colum erected in Memory of the Dreadfull Fire of London”.
The n seems to have been added back by classically educated scholars wanting to match the spelling of its Latin original. The pronunciation was unaffected, so the n has always been silent (in fact, it would be impossible to sound it following the m without making an extra syllable of it, as the Romans did). However, it is sounded in compounds like columnar.