ciṇ is the substitute of cli after the verb pad 'to go' when the affix ta follows.,
The affix त here means the third person singular tense-affix of the Atmanepada; as अपादि 'he went'; but not so in the dual and plural; as अपसाताम् 'they two went'; अपत्सत् 'they went'; अट् + पद + चिण् + त = अ + पाद् + त = अपादि (the affix त being elided by rule 6.4.104).,