The noun (Substantiv/Nomen) Rotstift is masculine in German. Therefore, the correct definite article in the nominative singular is der. So, you say: der Rotstift.
(red pen)
This word is composed and its gender is always determined by the root word.
Ein roter Stift, der traditionell zum Korrigieren oder Streichen von Texten verwendet wird; übertragen auch für Sparmaßnahmen.
A red pen, traditionally used for correcting or deleting texts; also used metaphorically for cost-cutting measures.
Der Rotstift wurde bei den Haushaltsplanungen angesetzt. / Der Lehrer benutzte den Rotstift, um die Fehler zu markieren.
The red pen was used in the budget planning. / The teacher used the red pen to mark the mistakes.
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 -ant are usually masculine. Common in words of Latin/French origin, often describing people or technical/scientific terms
Nouns ending in -ast are usually masculine. Usually found in scientific or technical terms, often from Greek/Latin origins
Nouns ending in -ich are usually masculine. Common Germanic suffix, often in everyday vocabulary and adjective-derived nouns
Nouns ending in -ig are usually masculine. Germanic suffix forming nouns from adjectives or verbs, often describing containers or enclosed spaces
Nouns ending in -ling are usually masculine. Forms nouns describing people or things with certain characteristics, often with diminutive or derogatory meaning
Nouns ending in -or are usually masculine. Latin origin, typically describing machines, devices, or professional roles
Nouns ending in -us are usually masculine. Latin/Greek origin, common in scientific, academic, and cultural terms
Strong Verb Nouns: Derived from strong verbs, describing the action itself or its result are usually masculine. Very reliable rule in German
Examples:
Cars: Car brands and models are generally masculine in German
Examples:
Currency: Most currency names are masculine, except for a few notable exceptions
Days, Months, and Seasons: These temporal nouns are consistently masculine
Male Persons: Nouns referring to male individuals are masculine
Examples:
Mountains and Mountain Ranges: Most mountain names are masculine, except for specific ranges
Non-German Rivers: Rivers outside German-speaking countries are typically masculine
Nouns ending in -gang are usually masculine. Typically describing paths or processes
Examples:
Nouns ending in -mut are usually masculine. Typically describing states or qualities
Examples: