Some Scholars argue that it is allowed to say Salam or Salamun as a greeting.
Shaikh Ibn ul-‘Uthaymeen rahimahullah said:
“…It is allowed for the wording of the greeting to be Salamun, and Salamun Alaykum. If he suffices with the statement (السلام), than there is no harm. For verily Ibraahim (may peace and blessings be upon him) when he returned the greeting to the Angels when they said: (سلاماً), he said (سلامٌ). That is: Upon you be peace. Likewise, a Muslim beginning the greeting with as-Salam or Salam, that is,( سلامٌ عليكم) or as-Salam that is: (السلام عليكم) then there is no harm in this…”
And Allah Knows Best
Faisal bin Abdul Qaadir bin Hassan