Aid to sailors - business taking turn (5,4)
I believe the answer is:
trade wind
'aid to sailors' is the definition.
I can't tell whether this defines the answer.
'business taking turn' is the wordplay.
'business' becomes 'trade' (trade is a kind of business).
'taking' says to put letters next to each other.
'turn' becomes 'wind' (I've seen this before).
'trade'+'wind'='TRADE-WIND'
Can you help me to learn more?
(Other definitions for trade wind that I've seen before include "Steady breeze towards the equator" , "shipowners once relied on" , "Flow of air" , "Current" .)