That breathes or respires. Now chiefly (of a gas or gases): used in or produced by respiratory gas exchange.
1A respirable substance; (originally) a food or substrate of cellular aerobic respiration; (later) a gas, especially air.
2A person who or thing which breathes or respires.
Late 16th century (in an earlier sense). From classical Latin respīrant-, respīrāns, present participle of respīrāre respire.