A salt reacts with ethanoic acid with a lot of effervescence and liberation of a colourless gas which turns lime water milky. This salt could be

The salt is sodium hydrogencarbonate.  ${\text{NaHCO}}_{\text{3}}$ reacts with acetic acid to form sodium acetate along with effervescence of  ${\text{CO}}_2$ gas and  ${\text{CO}}_2$  gas on passing through lime water turns milky.

${\text{CH}}_{\text{3}}\text{COOH}\left(aq\right)+{\text{NaHCO}}_{\text{3}}\left(s\right)\to {\text{CH}}_{\text{3}}\text{COONa}\left(aq\right)+{\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{CO}}_{\text{2}}\left(g\right)\uparrow$

$\text{Ca}{\left(\text{OH}\right)}_{\text{2}\left(\text{aq}\right)}+{\text{CO}}_{\text{2}\left(\text{g}\right)}\to \underset{\text{Milky\hspace{0.17em}white\hspace{0.17em}ppt}}{{\text{CaCO}}_{\text{3}\left(\text{s}\right)}}+{\text{H}}_{\text{2}}{\text{O}}_{\left(l\right)}$