The word engordasteis is the preterite form of engordar in the second person plural.
See the full engordar conjugation

engordar

Hasta engordasteis desde la última vez.
You even took on some weight since our last meeting.
Want to Learn Spanish?
Spanish learning for everyone. For free.
SpanishDict Premium
Have you tried it yet? Here's what's included:
Cheat sheets
No ads
Learn offline on iOS
Fun phrasebooks
Learn Spanish faster
Support SpanishDict