to express approval of or support for (something or somebody), esp publicly
to sign the back of (a cheque, bill, etc) as an instruction regarding payment, e.g. to another recipient
to write (a comment) on a document, esp on the back
Brit to record details of a motoring offence on (a driver's licence)
endorsable adj
endorsee /indawʹsee, endawʹsee/ noun
endorser noun
[alteration of obsolete endoss from Old French endosser to put on the back, from en-1 + dos back, from Latin dorsum]