use Symfony\Component\String\Inflector\EnglishInflector;

$inflector = new EnglishInflector();

$result = $inflector->singularize('zombies');   // ['zomby']

// src/Symfony/Component/String/Inflector/EnglishInflector.php

private const PLURAL_MAP = [
   // [...]

   // add the following 

   // zombies (zombie)
   ['seibmoz', 7, true, true, 'zombie'],

   // [...]
];