B1
In grammar, an irregular verb, noun, adjective, etc. does not obey the usual rules for words in the language.
Dictionary examples:
My brother's irregular use of 'gooder' and 'goodest' makes our parents laugh. (0.0)
My cat thinks 'meow' is an irregular verb and keeps saying 'meowed' instead of 'mewed'. (0.0)
My friend thinks 'funner' is the irregular comparative of 'fun'. (0.0)
a table of irregular verbs (24.6)