An archaic or poetic spelling of 'though,' meaning 'despite the fact that' or 'even if.'
Old English 'þeah' or 'þeauh,' showing up in Middle English texts as an alternative form. It's been largely replaced by 'though' in modern English.
Seeing 'tho' in old literature is like finding a linguistic fossil—it shows how much English pronunciation changed, since we eventually decided the 'gh' looked more important than the 'o' pronunciation.
Complete word intelligence in one call. Free tier — 50 lookups/day.