Almost everyone on board attending a dance (5)
I believe the answer is:
salsa
'dance' is the definition.
(type of dance)
'almost everyone on board attending a' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'everyone' becomes 'all' (all people).
'on' means one lot of letters goes inside another.
'board attending' becomes 'ss' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'all' with its final letter taken away is 'al'.
'al' inserted into 'ss' is 'sals'.
'sals'+'a'='SALSA'
Can you help me to learn more?
(Other definitions for salsa that I've seen before include "dancing?" , "Latin-American dance" , "hot stuff" , "This could be hot" , "Steps" .)