Nasty sort collaring navy over threat to shipping? (7)
I believe the answer is:
tornado
'nasty sort' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'collaring navy over threat to shipping?' is the wordplay.
'collaring' means one lot of letters goes inside another.
'navy' becomes 'RN' (abbreviation for Royal Navy).
'over threat' becomes 'oad' (I can't justify this - if you can you should give a lot more credence to this answer).
'shipping?' indicates putting letters inside (inserted letters are carried or shipped).
'rn' placed inside 'oad' is 'ornad'.
'ornad' going within 'to' is 'TORNADO'.
Can you help me to learn more?
(Other definitions for tornado that I've seen before include "A major blow" , "great deal of wind" , "Destructive windstorm" , "wind-up" , "Rapidly whirling column of air" .)