is

I

is, Irish, Old Irish is, Old Irish iss, Old Welsh iss, is = Greek $$Ge$$'stì; Latin est, is; English is, etc.

II

and, Irish, Early Irish is; seemingly an idiomatic use of is, is. Consider the idiom; "Nì e sin is mise an so" - "He will do it and I here"; literally: "He will do it, I am here". It is usually regarded as a curtailment of agus, and hence spelt variously as a's, 'us.