The Collaborative International Dictionary of English v.0.48:
Locum tenens \Lo"cum te"nens\n. [L., holding the place; locus place + tenens, p. pr. of tenere to hold. Cf. Lieutenant.] A substitute or deputy; one filling an office for a time. [1913 Webster]WordNet (r) 3.0 (2006):
locum tenens n 1: someone (physician or clergyman) who substitutes temporarily for another member of the same profession [syn: locum tenens, locum]