Hizo ademán de decir algo, pero mejor se quedó callado.

[morbrorper]

English Sentence

He made as if to say something, but instead kept quiet.

This in an interesting use of mejor: for “instead”, handier than “en cambio”, “en vez de eso”, etc.

[blogscot]

My suspicion is that mejor in this case would translate to “thinking better of it …”, but without some wider context it’s not possible to be certain.