what is secant modulus?
For the straight portion of the stress-strain graph, tangent modulus and secant modulus are the same.
When it starts curving, tangent modulus is the slope of the tangent, but secant modulus is the slope of the line joining the point to the origin.
In other words, tangent modulus is the marginal stress/strain, but secant modulus is the total stress/strain.
See http://www.instron.co.uk/wa/resourcecenter/glossaryterm.aspx?ID=99" for a fuller explanation, and a good diagram.
Separate names with a comma.