IPA: //sʌbˈtɛnənt//
KK: /sʌbˈtɛnənt/
A person who rents property from someone who is already renting it from the owner.
The subtenant signed a lease agreement with the main tenant.
Subtenant → It is formed from "sub-" (meaning under or below) and "tenere" (meaning to hold). A subtenant is someone who holds a lease or rental agreement under another tenant, thus being below them in the hierarchy of tenancy.
Think of someone who is 'holding' ('tenere') a lease 'under' ('sub-') another tenant — that's why a subtenant is someone who rents from another tenant.