He is an old-timer at this company, having worked here for twenty years.
Veteran employees sometimes resist new methods.
old stump; old roots
Original literal meaning: an old tree stump or roots. Now mostly used in figurative contexts or when discussing gardening/forestry.
Digging up the old stump in the garden is hard work.
古株 refers to a long-standing veteran member of a group, the direct opposite of a 新入り who has just joined.
古株 is a long-standing, established member, the opposite of a 新顔 who has just joined.
Compound of 古 (old) and 株 (stump, stock). Originally referred to an old tree stump, later extended metaphorically to a person with long-standing status.