The term ligand (ligare [Latin], to bind) was first used by Alfred Stock in 1916 in relation to silicon chemistry. It became more commonly associated with coordination chemistry following the publication of an article by H. Irving and R.J.P. Williams in Nature, 1948, 162, 746. For a fascinating review of the origin and dissemination of the term 'ligand' in chemistry see: W.H. Brock, K.A Jensen, C.K. Jorgensen and G.B. Kauffman, Polyhedron, 2, 1983, 1-7.
Ligands can be further characterised as monodentate, bidentate, tridentate etc. where the concept of teeth (dent) is introduced, hence the idea of bite angle etc.
The term chelate was first applied in 1920 by
Sir Gilbert T. Morgan and H.D.K. Drew [J. Chem. Soc.,
1920, 117, 1456], who stated:
"The adjective chelate, derived from the great claw or chela (chely- Greek) of the lobster or other crustaceans, is suggested for the caliperlike groups which function as two associating units and fasten to the central atom so as to produce heterocyclic rings."