There are multiple definitions - click on the translation that matches your context.

anticipo de honorarios

full

retainer

noun

Comparative law notes

Spain

that clients initially pay lawyers for future services

Definitions of retainer

English

an advance fee paid to a lawyer or other professional by a client. As the lawyer works on a matter, he or she will bill time against this fee.

Due to the expense of litigating this case, our attorney has requested a large retainer up front.