One rambling, greeting king and queen once (5)
I believe the answer is:
hiker
'one rambling' is the definition.
(a hiker rambles around)
'greeting king and queen once' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'king' becomes 'k' (chess abbreviation).
'and' is a charade indicator (letters next to each other).
'queen once' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'hi'+'k'+'er'='HIKER'
(Other definitions for hiker that I've seen before include "Someone walking (with backpack?)" , "I could be on the trail" , "One rambling" , "Trekker" , "Backpacker" .)