The noun diermēneutēs refers to an interpreter or translator — one who takes what is spoken in one language (or in a spiritual tongue) and renders it intelligible to others. In 1 Corinthians 14:28, Paul instructs that if there is no interpreter present, the tongue-speaker should remain silent in church.
Paul's instructions about interpretation in 1 Corinthians 14 reveal a profound theological principle: communication in the gathered church must build up the whole body, not only the individual. The spiritual gift of tongues without interpretation is self-edifying but not communally edifying. God desires intelligible speech that can be tested, understood, and acted upon. The interpreter's role is thus essential to the functioning of the body — making the mysterious accessible and building the community of faith.