Nasty moment, turning up topless (4,5)
I believe the answer is:
near thing
'nasty moment' is the definition.
The definition suggests a singular noun which matches the answer.
'turning up topless' is the wordplay.
'turning up' becomes 'unearthing' ('unearth' can be a synonym of 'turn up').
'topless' means to remove the first letter.
'unearthing' with its first letter removed is 'NEAR THING'.
Can you help me to learn more?
(Other definitions for near thing that I've seen before include "Even the short-sighted could plainly see that" , "Almost a nasty incident" , "Knife-edge event" , "almost a disaster" , "Narrow escape, close shave" .)