APOCOPATED FORMS OF THE ADJECTIVE

Some adjectives (not only qualify adjectives) are apocopated in their singular masculine form, when they go before the noun. The most frequent are:

A) Bueno, malo, alguno, ninguno, primero, tercero and postrero, lose the -o and cualquiera, lose the -a:
Un buen soldado / Cualquier día

B) Santo turns into San before a religious noun that doesn't begin with Do- o To-:
San Luis / Santo Domingo de la Calzada / Santo Tomás de Aquino

Grande turns into gran* :
Un gran banquete / Una gran fiesta

There is no difference between masculine or feminine in grande or gran.

C) Tanto and cuanto turn into tan and cuan when they go before an adjective, but no before a noun:
Tenía tanto sueño / Es tan importante
¿Cuánto dinero te has gastado? / No sabes cuán necesario es

This phenomenon doesn't exist in feminine, neither plural nor behind a noun:

Una mala compañera / Un día cualquiera / Los primeros clasificados