Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
postĕro, āvi, 1, v. a. [posterus].
Lit., to be behind or later, to come after,
Trop., to be inferior to, to want, to come short of, = ὑστερέω (post-class.): cum oliva tota nigrescet, quod speciei merito posteravit, fundendi ubertate compensat, Pall 12, 4.