The Greek adjective monos means only, alone, or solitary. It describes uniqueness (the 'only' God), isolation (being alone), or exclusivity (God 'alone' is worthy of worship). The adverb monon ('only') carries similar weight in statements of exclusive sufficiency: faith alone, grace alone, Christ alone.
Monos is foundational to monotheism and soteriology. The Shema's 'the LORD is one' (Deuteronomy 6:4) resonates in Paul's 'there is one God' (1 Timothy 2:5). Jesus's 'no one comes to the Father except through me' (John 14:6) uses the logic of monos: one way, one mediator, one Lord. The Reformation's sola (Latin for alone) — sola fide, sola gratia, solus Christus — is the doctrine of monos applied to salvation.