The words vindu and icchu are irregularly formed by the addition of the affix u , in the sense of 'agent having such a habit etc.'.,
To the verb विदि we add the augment नुम् and then the affix उ; as, विद् + नुम् + उ = विन्दुः (I. I. 47) वेदनशीलः 'intelligent'; so of इष् 'to wish', the ष is replaced by छ, and we have इच्छुः = एषणशीलः 'desirous'.,