From Middle Low German 'damp' (vapor, steam) — originally a noun for mine gases, then the moisture they left behind.
Slightly wet; moist.
From Middle Low German 'damp' meaning 'vapor, steam, fog.' Originally a noun for dangerous gases in mines (like 'firedamp'). The moisture left by vapor became the adjectival sense. Key roots: damp (Middle Low German: "vapor, steam").