Ni , Nid - Not
ni , nid - not ( ni is also used as a pronoun meaning 'we' or 'us'.)
N.B. Ni is the negative particle, equivalent to 'not' in English.
Ni is used before any verb that starts with a consonant.
Nid is used before any verb that starts with a vowel.
Nid is also used before any word that is not a verb.
It is a literary form and dim is far more commonly used for 'not' in spoken Welsh.