"The most famous university."
Translation:An ollscoil is cáiliúla.
Meaning of is(1) 3.(b), yes. When comparing (more than, the most), the adjective is always used in the "singular genetive feminine".
Using Tá + comparative adverbe (more than): Tá sé níos óige ná í: he is younger than her.
Using the copula to compare (more than): Is óige seisean ná í: He is younger than she is
Using the copula for superlative (the most): Is é an duine is óige : he is the youngest person. Tá sé ar an duine is deise acu: he is the nicest person among them.