Navigation system brings boy to a river (5)
I believe the answer is:
sonar
'navigation system' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'boy to a river' is the wordplay.
'boy' becomes 'son' (synonyms).
'to' means one lot of letters go next to another.
'river' becomes 'r' (abbreviation for river).
'son'+'a'+'r'='SONAR'
'brings' is the link.
Can you help me to learn more?
(Other definitions for sonar that I've seen before include "Echo-sounding equipment" , "Echo sounder - arson (anag)" , "echo device" , "location device" , "Underwater detection system" .)