Many nouns ending in -ma (from Greek origin) are masculine in Spanish.
Have a look and listen to these examples:
If you know the direct translation in English you can confirm if nouns have a "Greek origin" by checking if they have a cognate adjective ending in "-matic" (-mático/a in Spanish).
- drama = dramático/a
- problema = problemático/a
- idioma = idiomático/a
Forming the plural
To form the plural of these masculine nouns simply add an -s.