The story
From filth + -en, modelled after healthen, strengthen, lengthen, etc.
Etymology from Wiktionary, CC BY-SA 4.0.
filthen
Today it means: To cover with filth; besmut; besmirch; make filthy. Full definition →
Today it means: To cover with filth; besmut; besmirch; make filthy. Full definition →
From filth + -en, modelled after healthen, strengthen, lengthen, etc.
Etymology from Wiktionary, CC BY-SA 4.0.