see: ~ugh Usage: While never extremely common, ~ and thru have a long history of occasional use as spelling variants of ~ugh and through. Their greatest popularity occurred in the late 19th and early 20th centuries, when their adoption was advocated by spelling reformers. Their current use occurs chiefly in informal writing (as in personal letters) and in some technical journals.
THO
Meaning of THO in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012