IPA: /haɪˈpɒθɪkeɪtə/
KK: /haɪˈpɑːθɪkeɪtər/
A person who pledges something as security for a loan or borrowed money.
The hypothecator provided their property as collateral for the loan.
Hypothecator is formed from "hypotheca" (from Latin, meaning a pledge or mortgage) and "-tor" (a suffix indicating an agent or doer). The word refers to a person who pledges or mortgages property as security for a debt.
Think of someone who is making a 'pledge' ('hypotheca') and is the 'doer' ('-tor') of that action — that's why a hypothecator is someone who pledges property.