Old English cūþ

→ English could (mention)

→ English couth (inherited)

→ English selcouth (mention)

→ Old English uncuþ (affix)

→ Old English cuþlæcan (suffix)

→ Old English seldcuþ (prefix)

→ Old English hiwcuþ (compound)

→ Old Frisian kuth (cognate)