1951 R. S. Cahn et al. inJrnl. Chem. Soc. 3535Ring fission, with addition of a hydrogen atom at each terminal group thus created, shall be indicated by the prefix seco, the original steroid numbering being retained. 
1959 L. F. & M. Fieser Steroids iv. 156This was identified as the 2,3-secodicarboxylic acid..by saponification, oxidation to the 7-ketone, and Wolff-Kishner reduction to the known 2,3-secocholestane-2,3-dicarboxylic acid. 
1961 I. E. Bush Chromatogr. Steroids ii. 102The opening of rings to form seco-dicarboxylic acids. 
Ibid. vi. 342The C19 triols..are oxidized to the d-seco-16,17-dialdehydes. 
1977 Lancet 16 Apr. 841/1 The physiological regulation of secretion of this seco-steroid by the kidney. 
seco-
combining form 
Etymology: Latin secare to cut + English -o- 
 : having an opened ring  — in names of organic chemical compounds
< 2,3-secocholestane >
< 2,3-secocholestane >