What is the meaning of -ken?

alternative form of -ke

used to make diminutives

alternative form of -kan

Rōmaji transcription of けん

used to make diminutives

Forms verbs with an frequentative or intensive force from nouns or other verbs.

while, whilst, when, as

Assimilated form of -gan after the vowels E / İ / Ö / Ü.

Source: wiktionary.org