Word Family

A word family groups a base word with its inflections and transparent derivatives: help, helps, helping, helped, helper, helpful. Vocabulary research usually counts families rather than individual forms, because a learner who knows "help" gets the relatives nearly free. This is why "know 1000 words" is less daunting than it sounds: 1000 families, learned as base forms the way this site presents them, actually give you several thousand surface forms in real text.