A shortening of -shika miguu ya ("to fall at one's feet").
1) Used by an inferior to greet a superior.
From Wiktionary: https://en.wiktionary.org/wiki/shikamoo
Hello to an older person or authority figure.
Shikamoo (shee-kah-moh) (response: Marahaba). Some people frown on the use of Shikamoo because it started out as a servant's greeting to his/her master.
From Wikitravel: http://wikitravel.org/en/Swahili_phrasebook
It's typically used as a sign of respect, meaning 'I hold your feet' (signifying that you are beneath them). Marahaba as a response means 'You are welcome to'.
Another sign of respect is to hold your right elbow with your left hand when shaking the hand of an older person/authority figure.
The first time I got this wrong with "Welcome mother", the correct translation given was "Hello mother". This time, understanding the respect implicit in this greeting I typed "I greet you with respect mother" and was given "I respect you mother" as the correct translation.
My question: would you ever use this phrase in the middle of a conversation to show repect or is it only ever used as a greeting?
It is not only your mother; women old enough to have children can be addressed "mama" commonly; I used to be addressed as "dada"; young men as "kaka" and men as old as your father "baba" (same goes for "bibi"/"nyanya" in Kenya and "babu" or "mzee" ). They do not have to be related to you or even known previously.
Somtimes waiters and serving staff will hand things to you in the manner David mentions also (holding elbow with opposite hand). I wasn't sure of its meaning until now. I thought it might be submisive gesture - for example if you are being handeda knife, to signal good intention.