Not manifest, unseen, indistinct; uncertain, unclear
Adēlos (from a- privative + dēlos, 'manifest, clear') means 'not visible,' 'indistinct,' or 'uncertain.' It appears twice in the NT: (1) Luke 11:44, where Jesus compares the Pharisees to unmarked graves — tombs that are adēlos, not visible — which people walk over without knowing (incurring ritual uncleanness). (2) 1 Corinthians 14:8, where Paul says an uncertain (adēlos) trumpet call fails to prepare soldiers for battle.
The two uses of adēlos reveal opposite applications of the same word. In Luke 11, the hidden (adēlos) defilement of the Pharisees — their inward corruption masked by outward religiosity — is exposed by Jesus. What is hidden from human view is known to God; there is no adēlos before His sight (Hebrews 4:13). In 1 Corinthians 14, Paul argues for clarity in tongues and prophecy: an unclear (adēlos) sound fails its purpose. The Spirit's gifts are meant to edify — to build up — not to obscure. Both uses drive toward the same truth: clarity and transparency are the marks of genuine spiritual life.