I'll welcome correction if I'm wrong, but as I understand it in the modern calendar we have solemnities, feasts, and memorials, in decreasing order of precedence. Memorials are either obligatory or optional (although during Lent an obligatory memorial may only be celebrated as an optional memorial). Sundays rank behind all solemnities and behind feasts of the Lord, except in Advent, Lent, and Paschal Time, in which case they rank first, except that the transferable solemnities may be transferred to them and have precedence, though if not they are themselves transferred if they would fall on such a Sunday. Weekdays give way to solemnities and feasts, and are combined with memorials, except that all weekdays in Lent and from December 17 to 24 have precedence over memorials. Ash Wednesday and the Monday to Thursday of Holy Week are also weekdays, but take precedence over all other celebrations; and the days of the Octave of Easter all rank as solemnities of the Lord.

And I think it's not technically true that solemnities are feasts (though, definitely, not all feasts are solemnities). Before the major reforms of the calendar 1969, there were no "solemnities" at all, just feasts and commemorations, with feasts divided into I Class (e.g., the Epiphany), II Class (e.g., the Purification of the BVM), and III Class (e.g., St. Polycarp); I forget whether Commemorations (e.g., St. Blaise) were, strictly speaking, Feasts of the IV Class. Going back a little further, before 1960 feasts were divided, in decreasing precedence, into Doubles of the I and II Classes, Greater Doubles, and (Simple) Doubles, and before 1955 also Semidoubles.

So, that's a long way of saying that our current solemnities used to called feasts, so whether or not they still technically are, it's often customary, and I think completely acceptable, to refer to them as such.