convention, precedent, practice

newly arrived / newly joined / newly-entered

a greeting, a salutation, a polite set phrase / an address given at an official function or ceremony / greetings or respects such as given at holidays or funerals

to greet, to say hello, to address

an upperclassman / an older alumnus (graduate) of one’s school / a person who entered one’s workplace earlier; a senior; one who has seniority / an elder (one who is older)

member of a company

(business) a company

greeting

veteran, someone who is one's senior by a significant degree

regular employee, full-time employee