From the 16th century AD onward, English writers who were scholars of Greek and Latin literature tried to link English words to their Graeco-Latin counterparts. They did this by adding silent letters to make the real or imagined links more obvious. Thus det became debt (to link it to Latin debitum), dout became doubt (to link it to Latin dubitare), sissors became scissors and sithe became scythe (as they were wrongly thought to come from Latin scindere), iland became island (as it was wrongly thought to come from Latin insula), ake became ache (as it was wrongly thought to come from Greek akhos), and so forth.
English-language spelling reform - Wikipedia
