This is the 9198th most frequent German word.
maassen
The German word *"maßen"* means "to a certain extent" or "moderately." (*Note: "maassen" appears to be a misspelling.*)
'in Maßen' is an idiomatic usage meaning 'in moderation' or 'within reasonable bounds'.
Er lebt in Maßen, um gesund zu bleiben.
He lives in moderation to stay healthy.
'maßt sich an' is used here as a reflexive verb meaning 'presumes' or 'claims for oneself'.
Er maßt sich an, über alles Bescheid zu wissen.
He presumes to know everything.
'maßen' here is used in its verb form to mean 'to measure' or 'to assess' regarding quantity or value.