Eh, that's a great question. My Irish used to be good enough that I'd be able to answer that but I'm not sure what the direct translation would be. There is a word that's very close to "no" which is "níl" (neel) but in general it's short for "níl mé" (neel may - I am not).

In the present tense there is "tá" (taw) which is essentially short for "tá mé" (taw may - I am) but for example the answer to the question "Were you?" is "Ní raimh mé" (nee r-ow may) which is "I was not" but it is contextual. The pronunciation of "raimh" also varies by each of the 4 provinces along with every other word which is confusing as fuck. Some would say "rev" for "raimh".

In general it's the positive or negative of the verb though - were you? I was. Did you? I did. Will you? I will. Did she? She did etc.

Someone with better Irish may be along to hopefully make a show of me.

edit: Google translate says "ciallaíonn ní nach bhfuil" is "no means no" but there is no way in hell any actual Irish speaker would say those words when the context is so simple.

"ní nach bhfuil" (nee noch will) is "no is not", kinda. ciallaíonn is "means" straight up though.