Nouns which end in  -o, -or, -e, -i, -u, -y are normally Masculine
(Notable exceptions are la radio, la mano, la foto)

Nouns which end in  a, -tad, -dad, -ción, -sión, -zón are normally Feminine

Guess that ending :

Many English words have similar roots but different ending eg:

English 'ity' = Spanish 'dad' ... hospitality=hospitalidad, facility=facilidad

English 'ist' = Spanish 'ista' ... dentist=dentista, artist=artista

English 'ive' = Spanish 'ivo' ... offensive, expressive, positive = expresivo, positivo, efectivo