IPA: /ɪnˈdɔːrsər/
KK: /ɪnˈdɔrsər/
A person who endorses a document, especially a check or a bill of exchange, by signing it on the back to transfer ownership or rights.
The indorsor signed the check to transfer the funds to the new owner.
Indorsor is formed from "in-" (meaning in or on) and "dorsor" (from Latin "dorsum", meaning back). The term refers to a person who endorses or signs a document on the back, thus indicating support or approval.
Think of someone putting their name 'on the back' ('dorsum') of a document to show they support it — that's what an indorsor does.