The noun (Substantiv/Nomen) Online is neutral in German. Therefore, the correct definite article in the nominative singular is das. So, you say: das Online.
(online)
Der Zustand, mit dem Internet verbunden zu sein.
The state of being connected to the internet.
Ich bin den ganzen Tag online.
I am online all day.
German grammatical gender can be tricky at first, as it doesn't always seem logical - like with the neuter 'das Mädchen' (the girl). But here's the good news: Even though you won't find a rule for every word and some things just need to be memorized, there are quite a few helpful patterns and rules! These are real guideposts and can make your life significantly easier. So it's definitely worth knowing them!
Nouns ending in -chen are always neuter. This diminutive suffix makes things small or cute
Examples:
Nouns ending in -lein are always neuter. This diminutive suffix makes things small or cute
Examples:
Nouns ending in -icht are usually neuter. Found in abstract or collective nouns
Nouns ending in -il are usually neuter. Found in technical or scientific terms
Nouns ending in -it are usually neuter. Found in technical or scientific terms
Nouns ending in -ma are usually neuter. Found in abstract or technical terms
Examples:
Nouns ending in -ment are usually neuter. Found in abstract or technical terms
Examples:
Nouns ending in -tel are usually neuter. Found in fractional or diminutive terms
Examples:
Nouns ending in -tum are usually neuter. Found in abstract or collective nouns
Examples:
Nouns ending in -um are usually neuter. Found in abstract or technical terms
Examples:
Words with Ge- prefix: Often neuter, especially in collective or abstract nouns
Examples:
Exceptions:
Nouns ending with -nis and -sal: About 70% are neuter, often abstract or collective
Examples:
Foreign Loan Words (-al, -an, -ar, -är, -at, -ent, -ett, -ier, -iv, -o, -on): Often neuter, especially in technical or abstract terms
Alphabet Letters and Music Notes: Always neuter in German
Continents, Cities, Provinces, and Countries: Typically neuter, except for specific exceptions
Exceptions:
Gerunds and Parts of Speech as Nouns: Always neuter in German
Examples:
Hospitality Establishments: Names of hotels, restaurants, and cinemas are neuter
Nouns ending in -gut are usually neuter. Often describing goods or assets