-thek-?

[lilitaly]

Here's one I found while reading Thomas Bernhard's Der Stimmenimitator:

Pharmacist - Apotheker

Ok, BUT!

Librarian - Bibliothekar

Comments

[bradamant]

I would guess that the different endings have to do with the different endings of the base words: Apotheke versus Bibliothek.

[iloveyouohno]

Though I can't explain the change itself, I can say that something similar happens in English.

teacher
robber
traveller
worker
buyer

inspector
translator
director
donor
visitor
survivor
instructor
contributor
sailor
actor
collector

liar
beggar

Delicious~